Preheat oven to 375 deg F. Adjust rack to upper 1/3 of oven Brush mushrooms with melted butter, place rounded side down on an ungreased baking sheet.
Drain crab meat, discard liquid, set crab meat aside. In a medium bowl, stir together mayonaise and horseradish. Add bread crumbs, cheese, green onion and parsley, stirring until well mixed. Add crab meat and toss with a fork. Mound 1 level tablespoon of the mixture into each mushroom.
Bake 5 minutes or until warm, then broil 4" from the heat source for about 1 minute or until golden brown. Serve immediately. Microwave:
On a paper plate, lined with a paper towel, arrange mushrooms in a circle. Cover with waxed paper. Cook at 100% power (700w) for 2-3 minutes or until hot. Rotate plate once. Try 12 at a time.