2 1/2 teaspoons toasted sesame oil
1/2 pound Shiitake mushroom caps, sliced
1 small onion, sliced (optional)
1 clove garlic, minced (optional)
1 teaspoon minced ginger (optional)
1 head Napa cabbage, halved, cored and thinly slice crosswise
2 tablespoons soy sauce
1 tablespoon rice vinegar
2 teaspoons toasted sesame seeds