Heat oven to 350°. Remove stems from mushroom caps; reserve caps. Finely chop enough stems to measure about ½ cup. Discard remaining stems.
Mix chopped mushroom stems and remaining ingredients in small bowl until well blended. Spoon into mushroom caps, mounding slightly. Place in ungreased jelly roll pan, 15 ½ x10 ½ x1 inch.
Bake 15 to 20 minutes or until thoroughly heated. Serve warm.