Cook the sausage in a skillet over medium heat until browned and crumbled. Drain any excess fat.
Place the frozen hash brown potatoes in the bottom of the slow cooker.
Add the cooked sausage on top of the hash browns and sprinkle 1 cup of the shredded cheddar cheese over the sausage.
In a mixing bowl, whisk together the eggs, milk, salt, black pepper, and garlic powder until well combined.
Pour the egg mixture evenly over the layers in the slow cooker.
Sprinkle the remaining 1/2 cup of shredded cheddar cheese on top.
Cover and cook on low for 6 to 7 hours until the eggs are set and the casserole is hot throughout.