Preheat your oven to 400°F and generously grease a 12-cup muffin tin with cooking spray or butter.
In a large skillet over medium-high heat, cook the breakfast sausage until browned and crumbled, about 6-8 minutes, then drain excess fat and set aside.
In a medium bowl, combine the thawed and dried hash browns with melted butter, salt, and pepper, mixing well.
Divide the hash brown mixture evenly among the muffin cups, pressing firmly into the bottom and up the sides to create a cup shape.
Bake the hash brown cups for 12-15 minutes until edges are golden and crispy.
While cups bake, whisk together the eggs, garlic powder, and green onions in a bowl.
Remove muffin tin from oven, divide cooked sausage among the cups, then pour egg mixture over the sausage, filling each cup about 3/4 full.
Top each muffin with cheddar and mozzarella cheese, then return to oven and bake for 12-14 minutes until eggs are set and cheese is melted.