Easy Chicken and Spinach Breakfast Casserole

I’ve been making this chicken and spinach breakfast casserole on repeat lately, and it’s honestly become my go-to for meal prep Sundays. The combination of tender chicken, baby spinach, and tangy feta cheese creates such a satisfying breakfast that keeps me full for hours. Plus, it’s super easy to throw together and tastes even better reheated throughout the week!

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 1050-1200
• Protein: 120-135 g
• Fat: 55-65 g
• Carbohydrates: 35-45 g

Ingredients

For the chicken and vegetable base:

• 1.5 tbsp avocado oil
• 1 large white onion, diced into 1/2-inch pieces
• 5 garlic cloves, freshly minced
• 6 oz baby spinach
• 6 oz sun-dried tomatoes (sun-dried in oil, drained and chopped)
• 4 cups cooked chicken, shredded or cubed
• 1 tsp sea salt
• 1/2 tsp freshly cracked black pepper
• 1/4 tsp red pepper flakes

For the egg mixture:

• 6 large eggs
• 16 oz liquid egg whites
• 7 oz feta cheese, crumbled into 1/2-inch chunks

Step 1: Prepare the Oven and Mise en Place

• 1.5 tbsp avocado oil

Preheat your oven to 375°F and lightly grease a 9x13 inch baking dish with avocado oil or cooking spray.

While the oven heats, prepare all your ingredients: dice the onion into 1/2-inch pieces, mince the garlic cloves, chop the drained sun-dried tomatoes, crumble the feta cheese into 1/2-inch chunks, and measure out your cooked chicken.

Having everything prepped and ready will make the cooking process smooth and efficient.

Step 2: Build the Vegetable Base

• 1.5 tbsp avocado oil
• 1 large white onion, diced
• 5 garlic cloves, minced
• 6 oz baby spinach
• 6 oz sun-dried tomatoes, chopped
• 1 tsp sea salt

Heat the remaining avocado oil in a large skillet over medium heat.

Add the diced onion and cook for 5-8 minutes, stirring occasionally, until softened and translucent.

Stir in the minced garlic and cook for about 30 seconds until fragrant, then add the baby spinach and cook for 2 minutes, stirring constantly until the spinach is wilted.

Finally, mix in the chopped sun-dried tomatoes and sea salt, stirring well to combine all the flavors.

I like to let the garlic cook just briefly—too long and it can become bitter—so timing is key here.

Step 3: Combine the Filling in the Baking Dish

• vegetable mixture from Step 2
• 4 cups cooked chicken, shredded or cubed
• 1/2 tsp freshly cracked black pepper
• 1/4 tsp red pepper flakes

Transfer the sautéed vegetable mixture from Step 2 to your prepared baking dish, spreading it evenly across the bottom.

Add the cooked chicken and stir gently to distribute it throughout the vegetables.

Season with the black pepper and red pepper flakes, mixing everything together.

The chicken should be well distributed so every bite has protein and vegetables.

Step 4: Prepare and Pour the Egg Custard

• 6 large eggs
• 16 oz liquid egg whites
• 7 oz feta cheese, crumbled

In a large bowl, whisk together the 6 large eggs and 16 oz liquid egg whites until well combined and slightly frothy.

Pour this egg mixture evenly over the chicken and vegetable filling in the baking dish, then gently stir to incorporate everything and distribute the filling evenly throughout.

Sprinkle the crumbled feta cheese over the top, distributing it as evenly as possible.

The eggs will bind everything together into a cohesive casserole as it bakes.

Step 5: Bake Until Set and Golden

Place the casserole in the preheated 375°F oven and bake for 35-45 minutes, until the center reaches 190°F on an instant-read thermometer (this ensures the eggs are fully set and safe to eat).

The top should be lightly golden and the casserole should be firm when you gently shake the dish.

I recommend checking the temperature at the 35-minute mark rather than relying on time alone, since oven temperatures can vary.

Remove from the oven and let cool for 10 minutes before serving—this resting time allows the casserole to set up properly and makes it easier to cut into neat portions.

Easy Chicken and Spinach Breakfast Casserole

Delicious Easy Chicken and Spinach Breakfast Casserole recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 20 minutes mins

Cook Time 40 minutes mins

Total Time 1 hour hr 2 minutes mins

Servings: 8 servings

Calories: 1125

Ingredients Method

Ingredients

  

For the chicken and vegetable base:

• 1.5 tbsp avocado oil
• 1 large white onion, diced into 1/2-inch pieces
• 5 garlic cloves, freshly minced
• 6 oz baby spinach
• 6 oz sun-dried tomatoes (sun-dried in oil, drained and chopped)
• 4 cups cooked chicken, shredded or cubed
• 1 tsp sea salt
• 1/2 tsp freshly cracked black pepper
• 1/4 tsp red pepper flakes

For the egg mixture:

• 6 large eggs
• 16 oz liquid egg whites
• 7 oz feta cheese, crumbled into 1/2-inch chunks

Method

 

1. Preheat your oven to 375°F and lightly grease a 9x13 inch baking dish with avocado oil or cooking spray. While the oven heats, prepare all your ingredients: dice the onion into 1/2-inch pieces, mince the garlic cloves, chop the drained sun-dried tomatoes, crumble the feta cheese into 1/2-inch chunks, and measure out your cooked chicken. Having everything prepped and ready will make the cooking process smooth and efficient.
2. Heat the remaining avocado oil in a large skillet over medium heat. Add the diced onion and cook for 5-8 minutes, stirring occasionally, until softened and translucent. Stir in the minced garlic and cook for about 30 seconds until fragrant, then add the baby spinach and cook for 2 minutes, stirring constantly until the spinach is wilted. Finally, mix in the chopped sun-dried tomatoes and sea salt, stirring well to combine all the flavors. I like to let the garlic cook just briefly—too long and it can become bitter—so timing is key here.
3. Transfer the sautéed vegetable mixture from Step 2 to your prepared baking dish, spreading it evenly across the bottom. Add the cooked chicken and stir gently to distribute it throughout the vegetables. Season with the black pepper and red pepper flakes, mixing everything together. The chicken should be well distributed so every bite has protein and vegetables.
4. In a large bowl, whisk together the 6 large eggs and 16 oz liquid egg whites until well combined and slightly frothy. Pour this egg mixture evenly over the chicken and vegetable filling in the baking dish, then gently stir to incorporate everything and distribute the filling evenly throughout. Sprinkle the crumbled feta cheese over the top, distributing it as evenly as possible. The eggs will bind everything together into a cohesive casserole as it bakes.
5. Place the casserole in the preheated 375°F oven and bake for 35-45 minutes, until the center reaches 190°F on an instant-read thermometer (this ensures the eggs are fully set and safe to eat). The top should be lightly golden and the casserole should be firm when you gently shake the dish. I recommend checking the temperature at the 35-minute mark rather than relying on time alone, since oven temperatures can vary. Remove from the oven and let cool for 10 minutes before serving—this resting time allows the casserole to set up properly and makes it easier to cut into neat portions.