1 pkg. (6 oz.) frozen crabmeat, thawed, drained and flaked
Heat oven to 350°F.
Remove mushroom stems; chop enough stems to measure 1/3 cup. Discard remaining stems. Place mushroom caps, rounded sides down, in single layer in shallow baking dish.
Melt 1 Tbsp. butter in medium skillet on medium heat. Add onions and chopped mushrooms; cook 3 to 5 min. or until mushrooms are tender, stirring frequently. Stir in bread crumbs. Spoon into medium bowl. Add cream cheese; mix well. Stir in crabmeat.
Melt remaining butter; brush onto mushroom caps. Fill with cream cheese mixture.