Set oven control to broil. Spray 8-inch square (2-quart) glass baking dish with cooking spray.
Make Hamburger Helper mix as directed on box, using ground beef, milk and hot water.
Stir in mozzarella cheese. Transfer mixture to baking dish. In small bowl, mix bread crumbs and melted butter. Sprinkle on top of mixture in baking dish.
Broil with top about 4 inches from heat 2 to 4 minutes or until bread crumbs are golden brown and filling is bubbly. Cool 5 minutes before serving.