Heat the olive oil for the sauce in a medium saucepan and sauté the onions for 2 to 3 minutes. Drain maitake and reserve soaking water. Add all remaining ingredients except the shoyu and pasta. Cover, bring almost to a boil, reduce the heat to medium-low, and simmer for about 30 to 35 minutes. Add the shoyu and simmer another 5 minutes.
While the sauce is cooking, cook the pasta as package directs. When done, remove, drain and serve with sauce.
Per serving - 121 calories, 7 g fat (19% calories from fat), 11 g protein, 56 g carbohydrate, 12 g fiber, 0 mg cholesterol, 537 mg sodium