Remove mushroom stems and chop them finely. Transfer to medium bowl, stir in cheese, onion, and other ingredients. Blend well. Fill caps with mixture, mounding slightly in center. Sprinkle with paprika. Arrange in shallow baking dish. Cook in microwave on high until heated through, 4 to 5 minutes. Mushrooms can be filled ahead and refrigerated - if so, let stand 30 minutes prior to cooking.