Preheat oven to 350°. Combine first 4 ingredients; chill 2 hours. Stem and clean mushrooms. Fill mushroom caps with cream cheese mixture. Place mushrooms on lightly greased baking pan; sprinkle with additional Swiss cheese to taste. Bake at 350° for 18-25 minutes or until mushrooms are tender and cheese is melted. Serve warm. Makes about 6 servings.