Brown the ground breakfast sausage in a skillet. Once browned, reserve 1 tablespoon of the oil and dispose of the rest. Add the diced onions and peppers into the skillet with the reserved oil, saute over medium-heat until the onions and peppers are tender. Set aside.

Preheat oven to 375 degrees.

In a large mixing bowl, whisk together the eggs and milk. Add the browned sausage, onions and peppers and mix together. Stir in the shredded cheese and hash browns. Pour the mixture into a 9x13 baking dish. Bake for 20 minutes, then cover with aluminum foil and bake for another 10 minutes.

Allow the casserole to cool for 5-10 minutes, then serve.