The Healthy Egg Casserole You'll Want Every Morning

It can be a challenge to sneak in a healthy breakfast on busy weekday mornings. But registered dietician Kristen Carli of Mostly Green just may have the make-ahead meal hack to help you stay on track with a nutritious eating plan even when you're rushing out the door in the a.m. Meet her healthy egg casserole, which, as Carli told Mashed, "is a great meal prep dish for busy mornings." She adds, "I like making this on the weekend and then quickly grabbing a serving before heading to work." 

If you are lucky enough to linger over breakfast, Carli notes, "This is great served with a side of fruit and your morning coffee." 

Meanwhile, whether it's an on-the-go bite or a brunch with family or friends, this egg casserole comes together with just a few ingredients — and you may already have all of them on hand. The dish doesn't require a lot of time to prep or bake either. So, yeah, it's a win all around.

Gather some simple ingredients for this healthy egg casserole

For this colorful and healthy egg casserole dish, which is 100 percent vegetarian, you will simply need a yellow onion, diced, olive oil, a dozen eggs, whole milk, cherry tomatoes, spinach — fresh or frozen should work — as well as feta cheese, chopped chives, and salt and pepper. It doesn't get easier than that! 

We asked Carli about adding spice to the casserole if that is your preference, and as she told Mashed, "This recipe can handle heat if desired." She told us, "I recommend adding a half teaspoon of red chili flakes before baking. Alternatively, you could serve with your favorite hot sauce." Um, or both! It depends on just how hot you like your eggs and whether everyone you're serving appreciates spiciness

Meanwhile, once you have gathered your ingredients, honestly, you are halfway done with this recipe, with just a few steps left required to turn out a savory, protein-filled morning treat.

Sauté your onion for your healthy egg casserole

The first step in this healthy egg casserole recipe is to go ahead and preheat the oven to 400 degrees since this casserole is headed for a bake. Then, you will spray a large casserole dish with nonstick cooking spray to make cleanup much easier. 

Next, over medium heat, add olive oil to a small sauté pan. After a moment of allowing the oil to heat up, add your pre-diced onion and cook for several minutes, until the onion turns translucent. You can layer on some salt and pepper here if you'd like, since experts recommend salting your food at the beginning of cooking so the flavor has time to penetrate it. 

Then, remove the onions from the heat, and set the pan aside. You'll come back to it in a moment. Next, grab a large mixing bowl, and a whisk, and your carton of eggs.

Combine your eggs, veggies, and cheese for your healthy egg casserole

Crack your eggs now, and whisk them well to combine the yolks and whites. Although, as Carli told Mashed about her casserole dish, "You can definitely make this recipe with egg whites." Still, she added, "I would recommend using the whole egg for added protein and nutrients." After all, the recipe is called "healthy egg casserole."

Once your eggs are scrambled up, add in the milk and whisk again to combine. Then, in the same bowl — we love easy cleanup — you will add that cooked onion right in, as well as your tomatoes, spinach, feta cheese crumbles, the chopped chives, and more salt and pepper. Stir everything to combine all of the ingredients.

We asked Carli why she doesn't recommend heating the other veggies before the casserole hits the oven, and she told us, "Tomatoes will cook and the spinach will wilt very quickly, so this happens when the entire dish bakes."

Bake your healthy egg casserole

After all of your ingredients for this healthy egg casserole are combined, pour the mixture into the pre-sprayed casserole dish. You will bake the egg casserole for 30 minutes at 400 degrees Fahrenheit. Sure, you are ready to dig in once the meal comes out of the oven, but Carli recommends letting your creation stand for 15 minutes to make slicing easier. 

Meanwhile, if you do plan to heed her advice and make this meal ahead of time for the busy week ahead, note that, according to Carli, "Leftovers will last in an airtight container for up to four days in the fridge." You can either reheat your portion in the oven or microwave and head out the door with the confidence that you just started your day in the best way possible — with a healthy breakfast chock-full of protein and colorful veggies. 

And feel free to take this concept and run with it, experimenting with other veggies, cheeses, and even meats you enjoy.

The Healthy Egg Casserole You'll Want Every Morning
5 from 43 ratings
This egg casserole comes together with just a few ingredients — and you may already have all of them on hand. Try it out this weekend.
Prep Time
Cook Time
healthy egg casserole served
Total time: 55 minutes
  • ½ yellow onion, diced
  • 1 teaspoon olive oil
  • 12 eggs
  • 1 cup whole milk
  • 1 cup cherry tomatoes
  • 1 ½ cups spinach
  • ½ cup feta
  • 1 tablespoon chopped chives
  • 1 teaspoon salt
  • ½ teaspoon pepper
  1. Preheat the oven to 400 degrees Fahrenheit. Spray a large casserole dish with nonstick cooking spray.
  2. Heat a small sauté pan over medium heat. Add olive oil and allow to warm through. Add the onion and cook for several minutes until translucent.
  3. In a large mixing bowl, add a dozen cracked eggs. Whisk to combine.
  4. Add in milk, and whisk to combine.
  5. Add in cooked onion, tomatoes, spinach, feta, chives, salt, and pepper. Stir to combine.
  6. Add mixture to casserole dish and bake for 30 minutes. Let stand for 15 minutes before slicing.
Calories per Serving 100
Total Fat 6.5 g
Saturated Fat 2.7 g
Trans Fat 0.0 g
Cholesterol 167.6 mg
Total Carbohydrates 2.8 g
Dietary Fiber 0.4 g
Total Sugars 2.1 g
Sodium 218.3 mg
Protein 7.2 g
The information shown is Edamam’s estimate based on available ingredients and preparation. It should not be considered a substitute for a professional nutritionist’s advice.
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