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Summer Veggie Breakfast Casserole with Eggs

Summer veggie breakfast casserole with eggs baked in a golden, set custard over sautéed zucchini, peppers, tomatoes, and spinach. Each slice has tender vegetables and a cheesy, slightly puffed top.
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Prep Time 20 minutes
Cook Time 35 minutes
resting 5 minutes
Total Time 1 hour
Servings: 8 servings
Course: Breakfast
Cuisine: American
Calories: 390
Ingredients Equipment Method Notes

Ingredients
  

Vegetables
  • 1 zucchini diced
  • 1 yellow bell pepper diced
  • 1 red bell pepper diced
  • 1 cup cherry tomatoes halved
  • 0.5 lb red onion finely diced (½ cup)
  • 2 cup baby spinach roughly chopped
  • 2 clove garlic minced
  • 2 tbsp olive oil
  • 0.5 tsp salt divided
  • 0.25 tsp black pepper divided
Egg Custard
  • 8 large eggs
  • 0.5 cup whole milk
  • 0.5 tsp garlic powder
  • 0.5 tsp dried oregano
  • 0.5 tsp salt for custard
  • 0.25 tsp black pepper for custard
Cheese & Topping
  • 1.5 cup shredded sharp cheddar cheese divided
  • 0.25 cup crumbled feta cheese
  • 2 tbsp fresh basil chopped (for garnish)

Equipment

  • 1 sheet pan
  • 1 cast iron skillet

Method
 

Prep and cook the vegetables
  1. Preheat your oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish with olive oil or cooking spray. This helps prevent sticking before the vegetables and custard go in.
  2. Heat 2 tablespoons of olive oil in a large skillet over medium-high heat, then add the diced zucchini, red and yellow bell peppers, and red onion. Sauté for 5–6 minutes until softened and just beginning to pick up color at the edges.
  3. Add the minced garlic and baby spinach to the skillet and stir. Cook for 1–2 minutes until the spinach wilts, then season with salt and pepper and remove from heat.
  4. Fold in the halved cherry tomatoes. Spread the sautéed vegetable mixture evenly across the bottom of the prepared baking dish.
Build the casserole
  1. Scatter 1 cup of the shredded cheddar over the vegetables. It should form an even cheesy layer before the custard goes on top.
  2. In a large bowl, whisk together the eggs, whole milk, garlic powder, dried oregano, salt, and pepper until smooth and well combined. Whisking until fully blended helps the custard set uniformly.
  3. Pour the egg mixture evenly over the vegetables and cheese in the baking dish. Make sure the liquid reaches the edges so everything bakes at the same pace.
  4. Sprinkle the remaining ½ cup of cheddar and the crumbled feta over the top. The surface should look speckled with cheese before baking.
Bake and finish
  1. Bake uncovered for 30–35 minutes at 375°F (190°C), until the eggs are fully set in the center (no jiggle) and the top is golden and slightly puffed. A toothpick inserted in the center should come out clean.
  2. Remove from the oven and allow to rest for 5 minutes before slicing. The set custard firms up as it cools.
  3. Garnish with fresh chopped basil and serve warm. Add basil right before serving for the brightest flavor.

Notes

For the cleanest slices, let the casserole rest the full 5 minutes after baking, then lift portions with a wide spatula. Store covered in the refrigerator up to 3 days; reheat individual squares in the microwave until steaming. Freezing is not recommended because the custard texture can turn watery when thawed. For a dairy-light option, use reduced-fat cheddar and omit the feta or replace it with a small amount of nutritional yeast for a similar savory finish.