Preheat oven to 375
Cut sausage into 4 pieces. Cut each piece lenthwise and open so they can hold the mashed potato.Place on greased baking dish.
Fill each sausage with mashed potatos top with chopped onion and pepper add parmesan evenly over each portion and then add the shredded cheese evenly among them.
Bale uncovered 20 to 25 minutes until hot