1 tbsp red wine vinegar
salt, pepper to taste
1 garlic clove, minced
3 tbsp olive oil
4 portobello mushrooms, stems removed
1 6oz bag baby spinach
4 1/2 oz swiss cheese
Whisk together salt and pepper, vinegar, garlic and olive oil. Add portobelo and rub with marinade, then place on a baking sheet. Let sit for 15 minutes.
Bring water to a boil and blanch spinach for 20 seconds. Transfer to a bowl of ice water and then drain the spinach and squeeze dry. Chop spinach and toss with marinade.
Prepare a grill or skillet on medium high. Season mushrooms with salt and pepper, then grill top side down. Cook until browned and moist. Turn over and cook for 6+ minutes. Turn again to heat top and flip. Place cheese on top and cook until cheese melts. Add spinach to bottom half of hamburger buns and add mushroom top side up and serve.