This cheesy zucchini breakfast casserole is a perfect breakfast recipe filled with mozzarella cheese, fresh zucchini, and a delicious blend of dried herbs. It's low-carb, keto-friendly, gluten-free, and vegetarian, so it's a recipe that sure to please many diets.
Zucchini is in season from June through August, and it's one of my favorite summer vegetables. My go-to breakfast recipe year-round is pancakes, but this savory summer recipe is a seasonal favorite.
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This recipe calls for a few main ingredients (zucchini, onions, eggs, and cheese) and a beautiful blend of dried herbs.
- olive oil
- fresh zucchini
- sweet onion
- yellow mustard
- shredded mozzarella
- dried parsley
- garlic powder
- dried basil
- dried oregano
- black pepper
See the recipe card for quantities.
Preheat oven to 400°F.
In a large skillet, heat olive oil over medium heat. Cook the onion and zucchini until the zucchini is tender and the onions are translucent. Drain in a colander and allow the veggies to cool for 5–10 minutes.
Meanwhile, whisk the eggs, mustard, shredded mozzarella, and seasonings until combined in a large mixing bowl. When the zucchini has cooled slightly, stir in the zucchini/onion mixture.
Grease a 9x13 casserole dish. Pour in zucchini/egg mixture. Smooth over the zucchini so it lays flat.
Bake for 35 minutes or until eggs start to brown. Cover with foil and bake for an additional 10 minutes or until a knife is inserted into the center and comes out clean.
Let the cheesy zucchini casserole stand for 10 minutes before serving.
Substitutions & Variations
Here are a few ideas to remix this recipe to suit your taste (or your fridge contents!).
- Meat - this recipe would be absolutely delicious with the addition of sausage or bacon. For a casserole of this size, 1lb of breakfast sausage (cooked) or 5–6 slices of bacon (cooked) would be a good add-on.
- Cheese - I have made this with a blend of mozzarella and cheddar, and it turns out great. A little shredded parmesan would be lovely, too.
- Mustard - you can absolutely use spicy mustard or brown mustard or whatever kind of mustard you prefer. The mustard adds a little zing to the casserole.
- Seasoning - if you don't have basil and oregano, you could substitute these two with 2 teaspoon of Italian seasoning.
- Squash - yellow summer squash can be a good substitution, or it can be used alongside the zucchini.
If you're on the hunt for a vegan zucchini breakfast casserole, try Minimalist Baker's Vegan Zucchini Gratin.
This recipe calls for a 9x13 casserole dish.
If you're in a pinch, I have also made this split across two 9-inch pie plates (same bake time), but it's slightly too much filling, so you would have to leave some out. If you make this in a pie plate, I recommend putting the pie plate on top of a baking sheet to avoid a mess from overflow.
Store cheesy zucchini casserole covered in the refrigerator (baked) for three to four days or in the freezer (baked) for two to three months.
I have not tried to freeze this casserole unbaked yet, so I do not have any tips there for a make-ahead recipe, but if you try it, please let me know how it goes in the comments.
Watch the eggs for browning! At the end of the first 30 minute cook time, keep an eye on the casserole. If they start to brown sooner, go ahead and add that foil over the top to prevent over-browning.
Cheesy Zucchini Casserole
- 9x13 baking dish
- large skillet
- large mixing bowl
- 1 tablespoon olive oil extra virgin
- 8 cups thinly sliced zucchini about 6 medium
- 2 medium sweet onions sliced thinly
- 6 large eggs room temperature
- 1 tablespoon yellow mustard
- 4 cups shredded mozzarella cheese
- 1 tablespoon dried parsley flakes
- 1 teaspoon garlic powder
- 1 teaspoon dried basil leaves
- 1 teaspoon dried oregano leaves
- 1 teaspoon salt
- ½ teaspoon black pepper
- Preheat oven to 400°F.
- In a large skillet, heat olive oil over medium heat. Cook the zucchini and onion until the zucchini is tender and the onions are translucent. Drain in a colander and allow veggies to cool for 5–10 minutes.
- Meanwhile, whisk the eggs, mustard, shredded mozzarella, and seasonings until combined in a large mixing bowl. When the zucchini has cooled slightly, stir in the zucchini/onion mixture.
- Grease a 9x13 casserole dish. Pour in zucchini/egg mixture. Smooth over the zucchini so it lays flat.
- Bake for 30–35 minutes or until eggs start to brown. Cover with foil and bake for an additional 10 minutes or until a knife is inserted into the center and comes out clean.
- Let the cheesy zucchini casserole stand for 10 minutes before serving.
- Nutrition was calculated using MyFitnessPal.
- For 6 servings: 350 calories, 12g carbs, 21g fat, and 30g protein based on 6 servings.
- For 8 servings: 262 calories, 9g carbs, 16g fat, and 22g protein.
- Cook to a minimum temperature of 160 °F (71.1 °C)
- Do not use the same utensils on cooked food, that previously touched raw egg
- Wash hands after touching raw egg or egg shells
- Do not eat raw eggs
- Don't leave food sitting out at room temperature for extended periods
- Don't leave cooking food unattended
See more guidelines at USDA.gov.