Coat a small nonstick skillet with cooking spray; place over medium-high heat until hot. Add chopped peppers, celery, and onion; saute until tender. Remove from heat, and stir in chopped parsley.
Combine flour and 1/4 cup milk; stir until smooth. Combine flour mixture, remaining 3/4 cup milk, milk powder, and margarine in a large saucepan; stir well. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Remove from heat; stir in sherry, salt, and hot sauce.
Add vegetable mixture to sauce; stir well. Add crabmeat, stirring lightly. Spoon crabmeat mixture evenly into 4 gratin dishes coated with cooking spray.
Remove crusts from bread; cut each slice into 4triangles. Lightly toast bread triangles.
Arrange gratin dishes on a baking sheet. Bake crabmeat mixture at 375° for 15 minutes; arrange toast around edges of dishes. Bake 15 additional minutes or until crabmeat mixture is golden. Garnish with parsley sprigs, if desired.