1. Cook shells and cheese dinner according to basic package directions.
2. Stir half-and-half, 1/2 cup shredded cheese, and onion powder into shell macaroni mixture. Pour pasta mixture into an 8-inch square baking dish.
3. Remove crusts from bread with a serrated knife. Process bread slices in a food processor or blender until finely ground. Toss together breadcrumbs, Parmesan cheese, melted butter, and parsley.
4. Sprinkle shell macaroni with remaining 1/2 cup cheese and breadcrumb mixture.
5. Bake at 400° for 15 minutes or until pasta mixture is thoroughly heated. Let stand 5 minutes before serving.