Preheat your oven to 375°F (190°C) to ensure it reaches the proper temperature before baking. Lightly coat a 9×13-inch baking dish with non-stick cooking spray, making sure to cover both the bottom and sides of the dish. This helps prevent the casserole from sticking and allows each slice to be removed easily after baking.

Place a large non-stick skillet over medium heat. Add the turkey sausage to the skillet and cook for 6–8 minutes, using a spatula or wooden spoon to break it apart into small, bite-sized crumbles as it cooks. Continue stirring occasionally until the sausage is fully cooked and no pink remains. If there is excess grease in the pan, carefully drain it to keep the casserole from becoming overly oily.

Add the diced onions and bell peppers directly into the skillet with the cooked turkey sausage. Stir everything together and cook for 3–4 minutes, allowing the vegetables to soften and release their natural sweetness. The onions should become slightly translucent, and the peppers should be tender while still maintaining a bit of texture.

Stir the chopped spinach into the sausage and vegetable mixture. Cook for an additional 1 minute, stirring frequently until the spinach wilts and reduces in volume. Once the spinach has softened, remove the skillet from the heat and set the mixture aside to cool slightly. Allowing it to cool for a few minutes prevents the hot ingredients from partially cooking the eggs when combined later.

In a large mixing bowl, crack the eggs and whisk them thoroughly until the yolks and whites are completely combined and slightly frothy. Properly whisking the eggs helps create a lighter, fluffier casserole texture once baked.

Add the cottage cheese, garlic powder, onion powder, salt, and black pepper to the whisked eggs. Stir well until all the seasonings and cottage cheese are evenly distributed throughout the mixture. Small curds of cottage cheese are perfectly normal and will melt into the casserole as it bakes, adding extra creaminess and protein.

Carefully fold the cooked turkey sausage and vegetable mixture into the egg mixture. Add half of the shredded cheddar cheese and gently stir everything together until the ingredients are evenly combined. This ensures every serving contains a balanced amount of protein, vegetables, and flavor.

Pour the prepared mixture into the greased baking dish. Use a spatula or the back of a spoon to spread the mixture evenly across the dish so it bakes uniformly. Make sure the ingredients are distributed evenly from edge to edge.

Sprinkle the remaining shredded cheddar cheese evenly over the top of the casserole. This final layer of cheese will melt and create a delicious golden, slightly bubbly topping that adds both flavor and visual appeal.

Transfer the baking dish to the preheated oven and bake for 35–40 minutes, or until the center of the casserole is fully set and a knife inserted into the middle comes out clean. The top should be lightly golden, and the edges may begin to pull away slightly from the sides of the dish.

Remove the casserole from the oven and allow it to rest for 10 minutes before slicing. This resting period helps the casserole firm up, making it easier to cut into neat portions while also allowing the flavors to settle.

Slice the casserole into six equal portions and serve warm. Enjoy this protein-packed breakfast fresh from the oven, or allow the slices to cool completely before storing them for convenient meal-prep breakfasts throughout the week.