Preheat oven to 400*F. Coat a baking rack with cooking spray, then place the rack on a baking sheet and set aside. Butterfly each piece of chicken by slicing into the breast horizontally so you can open it like a book. Lay one quarter of the ham and cheese on one side of each breast, leaving 1/2 inch at edge uncovered, then close each piece. In a medium bowl, combine egg whites, buttermilk and mustard and blend until creamy. In a shallow bowl, combine bread crumbs, parmesan cheese, salt and pepper. Gently dip each piece of chicken in the crumb mixture, then into the egg white mixture, then again in the crumb mixture. Set on baking rack. Bake 30 to 35 minutes or until crisp and lightly browned, and chicken is no longer pink inside. Serve with lemon wedges.