Healthy Breakfast Casserole

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This healthy breakfast casserole is one of my favorite ways to start the day. It’s loaded with colorful veggies, protein-packed eggs, and just the right amount of melty cheese. It’s comforting, flavorful, and perfect for prepping ahead of time. Whether I’m feeding my family on a busy weekday or making brunch for guests, this recipe is always a hit!

I first made this casserole as a clean-out-the-fridge kind of meal, and it quickly became part of our regular breakfast rotation. It uses simple, whole ingredients like spinach, peppers, mushrooms, and eggs, and it’s super flexible, great for using up whatever produce you have on hand.

Not only is it easy to make, but it also happens to be naturally gluten-free, and so good for you thanks to all the veggies it’s filled with! Plus, you can bake it in a casserole dish for weekend brunch or divide it into muffin tins for quick, grab-and-go breakfasts during the week. However you serve it, this is one healthy breakfast recipe I know you’ll come back to again and again.

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🥘 Ingredients

Here’s what I use to make my healthy breakfast casserole. Everything is easy to find, and you can customize it based on what’s in your fridge.

Eggs: I use large eggs as the base of this casserole. They hold everything together and add a good dose of protein to keep us full all morning.

Veggies: I use a combination of mushrooms (my preference is button or cremini mushrooms), frozen spinach (thawed and squeezed dry), green and red bell peppers, and red onion. You can use any color bell peppers, yellow or white onions, any type of mushroom and fresh spinach if needed!

Seasonings: Simple seasonings are all that’s needed! I used fresh minced garlic, salt and pepper to add flavor to the sauteed veggies. If you don’t have fresh garlic, garlic powder will also work.

Milk Or Cream: For this version, I used heavy cream, but you can also use whole milk or half-and-half instead of heavy cream. You can also use a plant-based milk, just make sure it’s unsweetened and plain. Keep in mind that if you use a plant-based milk this casserole won’t be as rich.

Cheese: I love the combo of shredded cheddar and crumbled feta. You can swap in mozzarella, goat cheese, or whatever you have on hand. If you’re using shredded cheese, I recommend grating your own cheese for the best flavor and creamiest melt.

Olive Oil: I use both liquid and spray oil to cook the vegetables and coat the baking dish so the casserole doesn’t stick. Coconut oil or avocado oil would also work.

🔪 How To Make

My healthy breakfast casserole comes together in just a few simple steps. I usually prep the veggies the night before so I can get it in the oven first thing in the morning.

Prep: I start by preheating the oven to 350°F and lightly greasing a 7×11-inch casserole dish with olive oil or cooking spray.

Saute Veggies: In a large skillet, I heat the olive oil over medium heat, then add the diced onion. I cook it for 2–3 minutes until it softens, then stir in the garlic, bell peppers, and mushrooms. I let everything cook down until the veggies are tender and most of the moisture has evaporated, then remove the pan from the heat.

Whisk Eggs: While the veggies cool slightly, I whisk the eggs with milk, salt, and pepper in a large mixing bowl until fully combined.

Start Assembling: I drain any excess moisture from the cooked veggies and then spread them evenly into the bottom of the greased baking dish.

Layer: Then I layer the thawed and squeezed spinach on top. I pour the egg mixture over the veggies, making sure it’s evenly distributed.

Bake: Then I top everything with the shredded cheddar and crumbled feta. I bake the casserole uncovered for 35-45 minutes, or until the center is set and the top is lightly golden brown. I usually check it at 35 minutes, then give it a few more if the middle is still soft.

Cool: Once it’s done, I let it cool for 10 minutes so it firms up before slicing.

Serve: I cut it into 12 pieces and serve it warm, or save some for later in the week!

💭 Expert Tips

• Drain the cooked vegetables: To prevent the casserole from becoming too watery, drain the cooked vegetables before adding them to the casserole dish. 
• Defrost and remove excess water from the frozen spinach: The best way to remove excess water from frozen spinach is to defrost the spinach in a strainer and then squeeze it with your hands or use paper towels to press it until you’ve removed most of the moisture. Separate it with a fork because it will become compacted when squeezed.
• Grease casserole dish well: For the easiest serving, spray the dish well with oil or grease with butter. A well-greased dish will allow you to easily remove slices and not leave any of the good stuff behind due to sticking. 
• Use what you have: This is one of the most versatile breakfast recipes ever so don’t feel like you need to have exact ingredients. Make this casserole with almost any vegetable combination, so I love using what I have on hand and filling up this casserole with leftover veggies I need to use!

📖 Variations

• Extra Spicy: Adjust the heat to your personal preferences by adding red pepper flakes on top of the casserole before baking, ¼ teaspoon of Cayenne pepper to the eggs, or serve this dish with your favorite hot sauce.
• Additional Protein: To keep this a vegetarian keto casserole, you can add plant-based spicy sausage or breakfast sausage to this recipe for a sausage breakfast casserole. Just cook it with the onion and peppers and break it into small pieces with a wooden spoon as it cooks, then add the vegetable and sausage mixture to the casserole dish! If you eat meat, you can increase the grams of protein per serving with Italian sausage or ground sausage to make a keto sausage egg casserole.
• Egg Muffins: For breakfast egg muffins, follow the recipe as stated and use muffin tins for individual servings that are easy to reheat and freeze well. Transfer the egg mixture into an oiled 12-cup muffin pan. Preheat the oven to 350 degrees Fahrenheit and bake the muffins for 15 to 20 minutes. If you follow a low-carb diet or ketogenic diet, individual portions are an easy way to track your carbohydrate intake.
• Garnish: Before serving, garnish this easy low-carb breakfast casserole with freshly sliced green onions or fresh parsley.

🍽 Serving Suggestions

Enjoy by itself or serve with other breakfast foods. The casserole is filling on its own and has lots of nutrient-dense vegetables so it can stand alone or serve it with additional items. I like serving this low-carb breakfast casserole with fiber-rich smoothies, salads, and other favorite breakfast recipes for a larger spread. You can also serve it with a small serving of fruit for the kids!

🙌 Dietary Adaptions

This casserole is already vegetarian, gluten-free, and happens to be a diabetic friendly breakfast casserole recipe too! To make it into a dairy-free egg casserole, omit the cheese and use dairy-free milk in place of the heavy cream.

🫙 Storage Directions

• Storing: Leftovers keep in an airtight container in the refrigerator for up to four days.
• Reheating: Reheat this low carb vegetarian breakfast bake in a preheated oven at 350 degrees Fahrenheit for about 15 minutes. When heating from frozen, allow this dish to thaw overnight in the refrigerator.
• Freezing: Freeze leftovers for up to three months. Wrap individual pieces in plastic wrap or aluminum foil before placing them in a freezer-safe container.

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