When it comes to vegetarian breakfast recipes, an egg casserole checks all the boxes. It can easily be made ahead of time to be enjoyed on busy weekday mornings, or it can feed a crowd for brunch.

Baking dish with breakfast casserole topped with tater tots.

Plus, it’s loaded with veggies, and a creamy egg base. Even more so, those who typically enjoy sausage in their breakfast casserole won’t even miss a thing thanks to hearty mushrooms and spices like fennel seed and oregano. That’s right my friend, all the flavor, and totally meatless!

Ingredient Spotlight

One of the most beautiful things about a vegetarian breakfast casserole is that you can kind of throw whatever veggies you have on hand into it. So while I’ve tested these veggies with a purpose, feel free to mix and match as your heart desires.

Eggs in carton next to bowls of tater tots, kale, bell pepper, spices, parsley, cheese, mushroom, half and half, and onion.

Here are the VIP ingredients, but be sure to check the full recipe card below for all the details!

  • Mushrooms give the casserole a hearty, meaty texture, and add a rich flavor. I like baby bella mushrooms; white button mushrooms also work, or get fancy with another variety.
    • Diced or Sliced? I’ve tested it both diced and sliced, and it comes down to preference. If diced, they incorporate more into the casserole and it’s better for large mushrooms. Sliced is a pretty option for smaller caps.
  • Bell Pepper for color, texture, and flavor! I prefer a sweeter red variety, but yellow, orange, or even green are also delicious!
  • Kale is my green of choice. It’s true, I prefer kale over spinach, but if you don’t, you can absolutely use spinach in its place! Chop the kale before wilting it with the other veggies so it mixes into the casserole.
  • Spices are used for a sausage-like flavor that’s classic to breakfast casserole, without the meat! We’re using a blend of fennel seeds, oregano, sage, and thyme – all dried for ease. Oh, and red pepper flakes for flavor – they don’t come off spicy in the final product, but you can always leave them out if it’s a concern. Fresh parsley is also added for a flavor boost!
  • Tater Tots are the final *pièce de résistance*. Tested with both frozen hashbrowns and tots, the tots won (when don’t they?!). They get golden brown and crispy on top, yet blend into the casserole for a delicious potato bite. It’s a fun addition I learned thanks to Pip and Ebby.

How to Make Vegetarian Breakfast Casserole

Similar to a frittata, breakfast casserole doesn’t have a crust as quiche recipes do. However, the difference between a frittata and a breakfast casserole is that the casserole is baked in a large 9×13 pan instead of a pie dish. It’s generally served in square pieces, too, and can accommodate large groups with its serving size.

Yet all of them begin the same way: sauteing the veggies!

Saute the Vegetables

If you’ve been around here long enough (or for any recipe with mushrooms in it), then you know I love to start cooking mushrooms in a dry pan over medium heat. It’s a trick I learned from a chef way back when. This method allows the water to be released from the mushrooms without watering down the rest of the ingredients.

It also gets the mushrooms ready to absorb whatever flavor it takes on – in this case, our spices and herbs. If you consider “meat substitutes” this is it.

Once a majority of the water is released, the mushrooms with have reduced in size and the pan will mostly have dried up. Then, it’s time to melt in the butter and add the diced yellow onion, bell pepper, and spices to the mixture.

Don’t forget salt, too! You can always taste test at this point, which is a good idea since you won’t be able to season once it’s mixed with the eggs.

The final step is to wilt in the kale. Then, spread the veggies in the greased baking dish to cool off slightly while you prepare the eggs.

Whisk the Egg Base

Eggs are whisked together with half and half for a luxurious and creamy base. It’s my go-to addition for egg bakes, but you can substitute with whole milk if preferred.

Season the eggs, too. This is really important for flavor, otherwise, the majority of the dish will be bland.

Chef’s choice on when you would like to add the shredded cheese. I usually add it to the eggs but it can end up at the bottom of the bowl once poured (that is when I use thick farm-style shreds…they’re the best (not sponsored, but it is an affiliate link)).

It all gets mixed together so it’s not a big deal; otherwise, sprinkle them on top before adding the tots, or sprinkle it on the veggies before pouring in the eggs.

The Final Steps (and tots!)

Once the veggies have slightly cooled (you don’t want to cook the eggs yet!), pour the egg mixture into the pan. I recommend using a spoon or your whisk to gently make sure the veggies are mixed into the egg mixture.

Then, place the tots across the top of the casserole. Get fancy with a design, as we do in our Midwest Hotdish Casserole, or just dollop them around.

Breakfast casserole with tater tots on top before baking.

Bake the casserole uncovered until the center is set, the tots are golden, and the edges are slightly golden, too. The internal temperature should reach at least 160°F according to the FDA.

Serving Suggestions

When it comes to this meatless breakfast casserole, it’s satisfying enough to enjoy all on its own, which is exactly what I’ve been doing each morning thanks to making it ahead of time (more on that next).

But if you’re serving it for brunch or feeding hungry overnight guests, it pairs well with a spread of fresh fruit or homemade bagels. Of course, I can’t resist a caffeinated beverage – can you?! Cold brew in the summer, a hot latte when it’s cold out, please!

I also like to amp up the fresh veggies and garnish with some micro greens. They add a nice contrast and subtle fresh crunch.

Slice of vegetable breakfast casserole on top of pan.

Make Ahead & Storage Tips

Have I ever been so excited to share with you my tips for making a recipe ahead of time, and all of the freezing/storage/reheating tips?! I’m not sure I have.

This one tops the charts because of how versatile it is, and as a single lady, I appreciate that I, too, can make this large recipe and then have a nutritious savory breakfast to enjoy whenever I don’t feel like making myself breakfast!

Prepare it in Advance

There are two ways to make this casserole in advance: let it sit overnight unbaked, or bake and reheat it the next day.

To let it sit overnight unbaked, assemble just before you’re ready to put the tater tots on. Those need to wait until it’s time to bake or they’ll break apart overnight. So, cover the assembled casserole with plastic wrap and/or foil and place in the fridge overnight.

Remove from the fridge while the oven preheats (so you’re not putting a hot pan in a cold oven!!). Uncover, top with the tots – and extra cheese if you so choose – and bake according to the same directions.

To bake ahead of time, simply reheat the entire casserole or pieces of it until warmed through again. The entire casserole can be heated in the oven again, but I recommend covering it with foil so it doesn’t dry out in this case.

Slice of breakfast casserole on plate with fork taking bite.

Freezing Breakfast Casserole

This is a game-changer. Of course, I love freezing breakfast burritos, and you can’t go wrong with make-ahead breakfast sandwiches, but freezing an egg casserole is just so easy and reheating is a breeze.

To make weekday mornings easier, I recommend freezing individual pieces. Once they’ve cooled, wrap well in plastic wrap, and again in foil. This will help prevent freezer burn. The plastic wrap also ensures easy removal, as just foil tends to get stuck on the casserole.

Use the defrost setting on your microwave until the slice is thawed, then I like to heat on full power for about 30 seconds until fully heated through to at least 165°F. Time will vary depending on the size of your slice.

Frozen slices will last in the freezer for about three months and then will begin to lose their flavor.

Store Leftovers

To store any leftovers, place what’s left in an airtight container in the fridge. It will keep for about 3-4 days. Reheat in the microwave for about 1 to 1 minute 30 seconds until heated through. The filling is creamy enough that I haven’t had any issues with it drying out, but if you are concerned, place a few sprinkles of water on top before heating.

Did you make this recipe? Please leave a star rating and review in the form below. I appreciate your feedback, and it helps others, too!

Square of breakfast casserole on plate topped with microgreens.
5 (5 ratings)

Get the Recipe Mixed Vegetable Breakfast Casserole with Tater Tots

Whether it's a weekend brunch or make-ahead weekday breakfast, this Vegetarian Breakfast Casserole is loaded with mixed vegetables, topped with crispy tater tots, and elevated by the essence of fennel seeds for a sausage-like flavor without any meat!



  • Preheat oven to 375F and grease a 9×13 pan with cooking spray or softened butter.
  • Heat a large skillet over medium heat. Add the diced mushrooms to the pan in an even layer. Cook for 5-6 minutes and allow the water to release from the mushrooms, stirring occasionally as they lift from the pan.
    8 ounces baby bella mushrooms
  • Add the butter to melt, then stir in the yellow onion, bell pepper, garlic, and spices, as well as a good pinch of salt. Cook for 4-5 minutes until tender.
    2 Tablespoons unsalted butter, 1 cup yellow onion, 1 large bell pepper, 2 cloves garlic, ¼ teaspoon red pepper flakes, ½ teaspoon fennel seeds, ½ teaspoon dried oregano, ¼ teaspoon rubbed sage, ¼ teaspoon dried thyme
  • Stir the shredded kale into the vegetable mixture and cook fro 1-2 minutes until wilted, then, stir in parsley.
    2 cups kale, ¼ cup fresh parsley
  • Spread the veggies in an even layer across the baking pan to cool slightly. Meanwhile, whisk together eggs, half and half, cheese, salt and pepper.
    12 eggs, 1 ⅓ cups half and half, 1 cup shredded cheddar cheese, ½ teaspoon fine sea salt, Freshly ground black pepper
  • Pour the egg mixture into the veggies, stirring to combine as needed. If desired, sprinkle the top with extra shredded cheese, then top with the tater tots.
    45 Tater tots
  • Bake uncovered for 45-50 minutes or until tater tots are golden and the center of the casserole is set. The internal temperature should be at least 160°F. Let rest for 10-15 minutes, then slice and serve.
  • Store any leftovers in an airtight container in the fridge for 3-4 days. Reheat slices in the microwave for 1 – 1 1/2 minutes until heated through to 165°F.


  • Make Ahead Unbaked: store uncovered in the fridge without the tater tots. Remove from the fridge the next day while the oven preheats, add the tater tots, and bake according to the directions. Please see the post for more details as needed.
  • To Freeze: wrap slices well in plastic wrap, and again in foil. Place in the freezer. When ready to enjoy, unwrap and place on a plate. Use the defrost setting on your microwave until the slice is thawed, then I like to heat on full power for about 30 seconds until fully heated through to at least 165°F. Time will vary depending on the size of your slice.
Calories: 234kcal, Carbohydrates: 14g, Protein: 11g, Fat: 16g, Saturated Fat: 7g, Polyunsaturated Fat: 2g, Monounsaturated Fat: 5g, Trans Fat: 0.1g, Cholesterol: 187mg, Sodium: 400mg, Potassium: 350mg, Fiber: 2g, Sugar: 3g, Vitamin A: 2145IU, Vitamin C: 34mg, Calcium: 162mg, Iron: 1mg
Did you make this recipe?Please leave a star rating and review in the form below. I appreciate your feedback, and it helps others, too!