Heat oven to 375. Add the sausage to a medium saute pan. Cook over medium high heat until browned, crumbling the sausage with a spoon as it cooks.
Remove sausage with a slotted spoon and transfer to a large mixing bowl.
Reserve about 1 tablespoon of sausage grease from the saute pan, discarding the rest.
Add the onion and pepper to the saute pan and saute for 5 minutes until cooked. Add the garlic and saute for an additional 2 minutes until fragrant. If you are using the jarred red peppers, wait to stir them until after the garlic.
Pour the vegetable mixture into the mixing bowl with the sausage. Add the hash browns and 1 1/2 cups cheese to the mixing bowl with the sausage and vegetables. Stir to combine.
In a separate bowl, whisk together the eggs, milk, and black pepper until combined. Then add them to the hashbrown mixture and stir to combine. Pour the mixture into a baking dish, and top with the remaining 1/2 cup of shredded cheese.
Cover with aluminum foil and bake for 30 minutes and then remove foil and bake for an additional 10 to 15 minutes and the top of the potatoes begin to slightly brown. Remove and let the casserole rest for 5 minutes. Sprinkle with green onions if desired.