1. Heat an electric griddle to 275°.
2. Spread about 1 teaspoon mustard on 1 side of each bread slice. Top each of 4 bread slices (mustard sides up) with 1 cheese slice, 1/4 cup sauerkraut, and 2 ounces turkey. Top sandwiches with remaining bread slices (mustard sides down).
3. Coat both sides of sandwiches with cooking spray. Place on hot griddle, and cook 4 to 6 minutes per side or until cheese is melted.