Preheat the Oven: Preheat to 350°F (175°C) and grease a 9x13-inch baking dish.
Prepare Ingredients: Cook the sausage until browned and crumble it. Dice onions and peppers, and thaw hash browns.
Layer the Base: Spread the hash browns evenly in the greased baking dish. Top with sausage, onions, peppers, and 2 cups of cheddar cheese.
Whisk the Egg Mixture: In a large bowl, whisk together eggs, milk, salt, and pepper until smooth.
Pour and Top: Pour the egg mixture over the layers in the dish. Sprinkle the remaining 1 cup of cheddar cheese on top.
Bake: Bake for 45-50 minutes until the eggs are set and the top is golden brown. Let it rest for 5 minutes before slicing.