Cook pasta per package directions, rinse, drain and set aside. Place the 4 cup water, kombu and shiitake in a medium saucepan, cover and bring to a boil. Reduce flame to medium-low and simmer 4 to 5 minutes. Remove Kombu, set aside for soup stock or discard. Cover the pan and simmer another10 minutes. Reduce the flame to low, add the shoyu and simmer another 2 minutes.
Place the cooked soba in serving bowls, ladle the hot broth over and garnish each with toasted sesame seeds and scallions.
Per serving - 255 calories, 3 gram fat (11% calories from fat), 12 gram protein, 51 gram carbohydrate, 11 gram fiber, 0 milligram cholesterol, 490 milligram sodium