Preheat oven to 400°.
Clean mushrooms, and remove stems; finely chop stems.
Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add onions and garlic; sauté 1 minute. Add sausage, and cook until browned, stirring to crumble. Add the reserved mushroom stems, red pepper, salt, and black pepper; sauté 2 minutes or until stems are tender. Remove from heat; stir in cream cheese and breadcrumbs. Stuff 1 tablespoon sausage mixture into each mushroom cap. Arrange mushroom caps in a 13 x 9-inch baking dish coated with cooking spray; sprinkle evenly with Parmesan. Bake at 400° for 30 minutes or until lightly golden and thoroughly heated.