Preheat the oven to 350°F and lightly grease a baking dish with cooking spray.
Heat a skillet over medium-high heat. Brown the ground sausage, then drain any excess grease.
In a large bowl, combine the sausage, hash browns, onion, bell peppers, and 1 1/2 cups of shredded cheese.
Evenly spread the hash brown breakfast casserole mixture into the prepared baking dish.
In a separate bowl, whisk together the eggs, milk, spices, and seasonings until well combined.
Pour the egg mixture evenly over the casserole, then top with the remaining shredded cheese.
Bake the hash brown breakfast casserole for 55 to 65 minutes, or until the center is set.