Heat oil in a large, heavy skillet. Add tempeh, brown one side, flip over, and brown other side. Combine mustard, water, and shoyu. Mix and pour over tempeh. Cover, bring to a boil, reduce heat to medium low, and simmer 7 to 10 minutes. Remove lid, turn heat to high, and cook off remaining liquid. Place equal portions of tempeh, lettuce, tomato, and sauerkraut on each slice of bread and serve.
Per serving - 364 calories, 17 g fat (39% calories from fat), 24 g protein, 34 g carbohydrate, 3 g fiber, 0 mg cholesterol, 807 mg sodium