Preheat oven to 375°F (190°C) and grease a 9x13 inch baking dish with non-stick spray or butter.
In a large skillet over medium-high heat, cook the breakfast sausage until browned and crumbled, then drain the excess fat.
Spread the thawed hash browns in an even layer at the bottom of the prepared baking dish.
Distribute the cooked sausage evenly over the hash brown layer.
Sprinkle the shredded cheddar cheese uniformly over the sausage.
In a medium mixing bowl, whisk together the eggs, milk, salt, black pepper, onion powder, and garlic powder until well combined.
Pour the egg mixture slowly and evenly over the ingredients in the baking dish.
Bake for 40 to 45 minutes, or until the center is set and the top is lightly golden brown.
Remove from the oven and allow the casserole to rest for 10 minutes before slicing and serving.