Heat oil in a skillet, and sauté garlic and onions for 5 minutes. Mash the beans and add to the skillet. Add the diced tomatoes and shoyu. Add some bean and tomato cooking liquid, if needed, for the right consistency. Cover, reduce the flame to low, and simmer for 15 to 20 minutes.
For a delicious variation, add red or green bell peppers.
Per serving - 80 calories, 2 g fat (19% calories from fat), 4 g protein, 15 g carbohydrate, 6 g fiber, 0 mg cholesterol, 119 mg sodium