Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
In a large skillet over medium heat, cook the turkey sausage until browned and crumbled, about 5-7 minutes. Drain excess fat and set aside.
In a large mixing bowl, whisk together softened cream cheese and eggs until smooth. Add milk, garlic powder, onion powder, salt, and pepper; whisk to combine.
Add thawed hash browns, cooked sausage, and shredded cheddar cheese to the egg mixture. Gently fold until evenly combined.
Pour mixture into the prepared baking dish, spreading evenly. Sprinkle chopped green onions on top if desired.
Bake in the preheated oven for 45-50 minutes, or until set in the center and golden brown on top. Check doneness by inserting a knife or toothpick; it should come out clean.
Let the casserole cool for a few minutes before slicing. Serve warm and enjoy!