Preheat oven to 400°F. Grease a baking dish and set aside.
In a small bowl, mix together onion, bell pepper, garlic powder, paprika, and cayenne pepper. Set aside.
Slice each chicken breast in half horizontally to create 4 thin cutlets. Place cutlets between two pieces of wax paper and pound with a meat mallet until about 1/4-inch thick.
Brush each cutlet with melted butter and season both sides with salt and pepper.
Spread cream cheese onto each cutlet and top with the onion mixture. Roll up the chicken breasts and place seam side down in the prepared baking dish.
Brush the tops of the chicken breasts with remaining butter and sprinkle Parmesan cheese over top. Bake for 25 minutes or until cooked through.