Preheat your oven to 350°F. Grease a 9x13-inch baking dish with olive oil.
In a large mixing bowl, whisk together the eggs, milk, salt, black pepper, garlic powder, and onion powder until well combined.
Stir in the cooked ground turkey, diced bell peppers, chopped spinach, and half of the shredded cheddar cheese into the egg mixture.
Pour the mixture into the prepared baking dish and spread it evenly.
Sprinkle the remaining cheddar cheese on top.
Bake in the preheated oven for 30-35 minutes, or until the eggs are set and the top is lightly golden.
Let the casserole cool for about 5 minutes before slicing and serving.