Preheat your oven to 350°F (175°C) to ensure a perfectly baked Casserole.

Grease a 9x13 inch baking dish with cooking spray or butter.

In a large mixing bowl, combine the frozen hash browns, diced onion, chopped bell pepper, and breakfast sausage (if using). Stir in the shredded cheddar and mozzarella cheeses.

In a separate bowl, whisk together the eggs, milk, garlic powder, salt, black pepper, and paprika until smooth.

Pour the egg mixture over the hash brown mixture and gently stir to combine.

Spread the combined mixture evenly into the prepared baking dish.

Sprinkle the reserved cheese mixture evenly over the top of the casserole.

Place the baking dish into the oven and bake for 45-50 minutes until the center is set and the top is golden brown.

Once baked, allow the casserole to cool for about 10 minutes before serving. Garnish with sliced green onions if desired.