Begin by preheating your oven to 400 degrees and then wash the bell peppers.
Slice the bell peppers length-wise, remove the membranes, add a pinch of salt and pepper to season them, and put them on a greased oven safe tray or dish. In a large non-stick skillet, brown the Italian sausage with the onions.
Once the sausage is browned, drain any excess fat, add the cream cheese to the skillet and mix well.
Stuff the peppers with the sausage, cream cheese, and onion mixture.
Top the peppers with mozzarella cheese and bake at 400 degrees for 15 minutes or until cheese is melted.