Combine mustard and honey in a small bowl. Spread one side of each of 4 bread slices with 1 1/2 teaspoons mustard mixture.
Place one cheese slice on dressed side of bread slices; top each with 4 or 5 apple slices and 2 ounces turkey. Top sandwiches with remaining 4 bread slices. Coat both sides of sandwiches with cooking spray.
Heat a large nonstick skillet over medium-high heat. Add sandwiches to pan. Cook 2 minutes on each side or until bread is browned and cheese melts.