Feta Portobello Burgers

2 hamburger rolls
2/3 cup baby lettuce leaves or baby spinach
2 large tomato slices, ½ inch thick
1/3 cup crumbled Feta (goat or bleu cheese if you prefer)
2 portobello mushrooms, stems removed
4 Tablespoons olive oil
1 Tablespoon balsamic vinegar
2 cloves garlic
1-1/2 cup thin sliced red onion
2 Tablespoons water
¼ cup red wine (optional ingredient but wine will add richness to onions)

Whisk garlic, vinegar, 2 Tablespoons oil, and a pinch of salt together in a small bowl.  Brush the mixture generously on both sides of the mushrooms.  Allow to stand for 30 minutes.

Meanwhile, heat the remaining oil in a heavy skillet and add the onions.  Cook over medium heat, stirring frequently until the onion is brown and very soft (10-15 minutes).  Add water and wine.  Cook over low heat until the liquid is mostly evaporated.  Salt and pepper to taste. 

Heat grill to medium.  Grill the mushrooms, gill side down for 4-5 minutes. Turn over and top each mushroom cap with half the cheese.  Grill top side down for 4-5 minutes.  Mushrooms should be tender.  

Toast buns, cover with onions, and place one mushroom cap on the bottom half of each roll.  Top the mushroom with lettuce and tomato.  Replace top of roll.  Serves 2.