Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the thawed hashbrowns, cooked sausage, and shredded cheddar cheese. Mix well.
In a separate bowl, whisk together the milk, eggs, garlic powder, onion powder, salt, and pepper until fully combined.
Pour the egg mixture over the hashbrown and sausage mixture, stirring until everything is evenly coated.
If using, fold in the diced green onions.
Grease a 9×13 inch baking dish and pour the mixture into the dish, spreading it out evenly.
Bake in the preheated oven for 45-50 minutes, or until the casserole is set and the top is golden brown.
Let it cool for about 10 minutes before serving.
