
Ingredients
- 4 large portobello mushroom caps (about 16 ounces total)
- 1/3 cup balsamic vinegar
- 1/2 cup water
- 1 tablespoon sugar
- 1 garlic clove, minced
- 1/4 teaspoon cayenne pepper (optional)
- 2 tablespoons olive oil
- 4 whole-wheat buns, toasted
- 4 slices tomato
- 4 slices red onion
- 2 bibb lettuce leaves, halved