Cut tofu into chunks and place in a flat dish with sides. In a small bowl, combine garlic, ginger, soy sauce, and vinegar. Pour marinade over tofu and toss to coat. Marinate for an hour.
Spoon tofu and marinade into large skillet and add mushrooms and stock. Bring to a boil, then reduce heat to low. Simmer, uncovered, until tofu is cooked through and stock is reduced by half, 10 minutes.
Add sesame oiland serve hot, sprinkled with scallions.This makes a nice main dish when served over rice with a side dish of clear soup and a marinated vegetable salad.Servings: 4