Preheat the oven to 350°F (175°C) and grease the 9x13 inch baking dish.
In a skillet over medium heat, cook the breakfast sausage until browned and fully cooked. Drain excess fat if necessary.
In a mixing bowl, whisk together the eggs, milk, salt, pepper, onion powder, and garlic powder until well combined.
In the greased baking dish, spread the frozen hash browns evenly across the bottom.
Layer the cooked sausage over the hash browns, followed by 1 cup of the shredded cheddar cheese.
Pour the egg mixture evenly over the entire casserole.
Sprinkle the remaining 1 cup of cheddar cheese on top.
Bake in the preheated oven for 45 minutes or until the cheese is melted and bubbly, and the eggs are set.
Allow the casserole to cool slightly before garnishing with chopped green onions if desired. Serve warm.