These make a great stand-in for burgers, or slice them to stuff in a tortilla or lettuce wrap. What portobello mushrooms lack in beauty they make up for in taste, especially when marinated with garlic. You can tell that the mushrooms are done when they’re pliable all the way through.
Wipe mushrooms with a damp towel. Carefully remove mushroom stems by popping them off, and gills, by scraping with a tablespoon, and set them aside. (You can add them to stock or use them for another recipe.)
Combine the remaining ingredients in a zippered bag or shallow baking dish. Add mushrooms and marinate for 1 hour, flipping mushrooms halfway through.
Heat a grill pan or grill over medium heat.
Remove the mushrooms from the marinade and place on the hot pan or grill, gill side down. (You can cook down the marinade to make a balsamic glaze if you like.)
Let mushrooms cook for 5 minutes and then flip so cap side is in contact with pan or grill. Let cook another 5 minutes or until the cap is pliable and cooked through. You will likely see liquid pooling in the mushroom cap, which means that the mushroom is getting cooked through. It might be as much as 15 minutes total.
Serve the mushroom whole on a bun, or sliced with lettuce, tomato and red onion in a tortilla or green leaf as a wrap.