Preheat oven to 375°F (190°C).
Grease a 9×13-inch baking dish.
Cook the breakfast sausage until browned and drain excess grease.
Spread the hash browns evenly into the baking dish.
Sprinkle the cooked sausage over the hash browns.
Add the shredded cheddar and mozzarella cheese evenly.
In a large bowl, whisk together eggs, milk, garlic powder, onion powder, paprika, salt, and pepper.
Pour the egg mixture evenly over the casserole.
Sprinkle chopped green onions on top.
Bake for 45–50 minutes or until the center is set and the top is golden.
Let the casserole rest for 10 minutes before slicing.
Serve warm and enjoy.