Preheat the oven to 350°F. Grease a 9x13-inch baking dish with cooking spray.
In a large mixing bowl, whisk together the eggs, milk, salt, pepper, garlic powder, and onion powder until well combined.
Add the crumbled sausage, thawed hash browns, shredded cheddar cheese, diced bell pepper, and diced onion to the egg mixture. Stir until all ingredients are evenly coated.
Pour the mixture into the prepared baking dish, spreading it out evenly.
Bake in the preheated oven for 45-50 minutes, or until the casserole is set in the middle and lightly golden on top.
Let the casserole cool for about 10 minutes before slicing and serving.