Cook 6 slices chopped bacon; drain on paper towels. Pour off excess fat & add 1 cup finely chopped onion & 1 finely chopped celery rib; cook until softened. Stir in 1/2 cup finely chopped apple, 1 finely chopped slice toasted sandwich bread & the bacon. Fill 16 white stuffer mushrooms. Bake in 375 degree oven for 15 minutes.