Preheat oven to 350°.
Melt butter in a nonstick skillet over medium-high heat. Add onion, bell pepper, and garlic; sauté 5 minutes or until tender. Stir in cottage cheese and Worcestershire sauce, stirring until cheese melts. Remove from heat; stir in breadcrumbs. (Mixture will be thick.) Spoon mixture evenly into mushroom caps.
Place the mushroom caps in an 11 x 7-inch baking dish coated with cooking spray. Sprinkle mushrooms evenly with paprika. Bake at 350° for 20 minutes or until tender. Sprinkle with Parmesan cheese.