4 large Portobello mushroom caps (approximately 5 inches in diameter)
1/3 cup balsamic vinegar
½ cup water
1 tbsp sugar
1 garlic clove, minced
¼ tsp cayenne pepper, optional
2 tbsp olive oil
4 whole-wheat buns, toasted
4 slices tomato
4 slices red onion
2 Bibb lettuce leaves, halved
Clean mushrooms with a damp cloth and remove stems. Place in a glass dish, stem (gill) side down.
To prepare the marinade, in a small bowl whisk together the vinegar, water, sugar, garlic, cayenne, and olive oil. Drizzle the marinade over the mushrooms. Cover and marinate in refrigerator for about 1 hour, turning once.
Grill mushrooms for about 5 minutes, turning a couple times, until tender and serve on whole-wheat bun topped with lettuce, tomato, and red onion.
