Preheat the oven to 350°F (175°C).
In a large skillet over medium heat, cook the breakfast sausage until browned and fully cooked, breaking it apart with a spatula as it cooks. Drain any excess grease.
In a large mixing bowl, combine the softened cream cheese, eggs, milk, garlic powder, onion powder, salt, and pepper. Whisk until smooth and well combined.
In a greased 9x13-inch baking dish, spread the frozen hashbrowns evenly across the bottom.
Layer the cooked sausage over the hashbrowns, followed by the egg and cream cheese mixture.
Sprinkle the shredded cheddar cheese on top.
Bake in the preheated oven for 45-50 minutes, or until the casserole is set and the top is golden brown.
Remove from the oven and let it cool for 5-10 minutes before serving. Garnish with chopped green onions if desired.