Heat oil in a medium saucepan and sauté onions for 1 to 2 minutes. Add carrot and bell pepper and sauté for 3 minutes. Add all remaining ingredients except the udon and shoyu. Cover, bring to a boil, reduce the flame to medium-low and simmer 20 minutes until the mushrooms are tender. Cook the udon per package directions, rinse, drain and set aside. Add the shoyu to the sauce and simmer another 5 minutes before serving over udon.
Per serving - 389 calories, 9 g fat (19% calories from fat), 21 g protein, 63 g carbohydrate, 13 g fiber, 0 mg cholesterol, 639 mg sodium