Preheat your oven to 350°F (175°C).
In a large skillet, cook the breakfast sausage over medium heat until browned.
In a large mixing bowl, whisk together the eggs, milk, salt, and pepper until well combined.
Add the cooked sausage, hash browns, bell peppers, green onions, and cheddar cheese to the egg mixture.
Grease a 9x13 inch baking dish and pour in the mixture, spreading it evenly.
Bake in the preheated oven for 40-45 minutes or until the casserole is set and the top is golden brown.
Allow the casserole to cool for 10 minutes before serving.