- 1/3 cup soy sauce
- 2 tablespoons mirin (sweet Japanese rice wine) or medium-dry Sherry
- 3 tablespoons rice vinegar
- 1 1/2 tablespoons minced peeled fresh gingerroot
- 2 tablespoons sugar
- 4 fresh Portobello mushrooms (about 1/4 pound each), stems trimmed flush with caps and reserved for another use
- 2 tablespoons mayonnaise
- 2 teaspoons rice vinegar
- 1 teaspoons Asian sesame oil
- 1/2 teaspoon honey
- 2 cups finely shredded Napa cabbage
- 1/2 cup finely shredded carrot
- 2 scallions, chopped fine
- vegetable oil for brushing mushroom caps
- 4 sesame-seed hamburger buns, split and toasted lightly
- available at most Asian markets, specialty foods shops, and some supermarkets
- In a small saucepan simmer marinade ingredients, stirring until sugar is dissolved. Continue simmering marinade until reduced to about 1/2 cup and cool to room temperature.
- Put mushroom caps and marinade in a large sealable plastic bag, arranging caps in one layer, and seal bag, pressing out excess air. Marinate mushrooms at room temperature, turning bag over several times, 1 hour.
- In a bowl whisk together mayonnaise, vinegar, oil, and honey and add cabbage, carrot, and scallions. Toss vegetables well to coat and season with salt and pepper.
- Preheat broiler.
- Drain mushrooms and arrange, stemmed sides up, on lightly oiled rack of a broiler pan. Broil mushrooms 2 inches from heat and turn over. Brush mushrooms lightly with oil and broil 3 minutes, or until tender. Transfer mushrooms with a slotted spatula to hamburger bun bottoms. Top mushrooms with slaw and bun tops.