Apple-Kraut Tuna Sandwich

1 (5 ounce) can tuna in water, drained

¼ cup sauerkraut

¼ cup finely chopped apple

2 tablespoons Dijon mustard

1 tablespoon red wine vinegar

4 slices whole wheat bread, toasted

Mix tuna, sauerkraut, apple, Dijon mustard, and red wine vinegar in a bowl. Serve on toasted wheat bread.