Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, cook the breakfast sausage until browned. Break it apart with a spatula. Add the diced onion and bell pepper, cooking until the vegetables are softened, about 5 minutes. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the eggs, milk, garlic powder, salt, black pepper, and smoked paprika until well combined.
Stir the cooked sausage mixture into the egg mixture. Then, gently fold in the frozen hash browns and 1 cup of shredded cheddar cheese.
Grease the 9x13 inch baking dish with cooking spray or oil. Pour the hash brown and egg mixture into the dish, spreading it evenly.
Sprinkle the remaining 1 cup of shredded cheese on top.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes. Remove the foil and bake for an additional 15 minutes, or until the top is golden brown and the casserole is set in the middle.
Allow to cool for 5-10 minutes before slicing. Serve warm and garnish with chopped green onions if desired.