Preheat the oven to 350°F. (If making this recipe overnight, see note below.)
Add the oil to a skillet over medium high heat. Brown and crumble the sausage for 5 - 7 minutes. Drain and set aside.
In a large bowl, whisk together the eggs, milk, salt and pepper.
Stir the hash browns, 1 ½ cups cheese, bell pepper and sausage into the egg mixture.
Grease a 9 x 13 baking dish with nonstick cooking spray or butter. Pour the egg mixture into the baking dish, spread it into an even layer and top with the remaining cheese.*
Bake the casserole for 40 minutes and then loosely cover it with foil (to prevent browning) and bake for 15 - 20 minutes more, until cooked through. To test for doneness, a fork poked into the middle of the casserole should come out dry (with no wet egg on it).
Cool for 5 - 10 minutes before serving. Optionally, garnish with chopped parsley.