Ideal for those who suffer from food allergies, these mini burgers show off the simple beauty of a grilled portobello mushroom: the smokiness of the grill and the tang of a balsamic marinade. Topped with red onion and tomato, and you’ll practically forget you’re eating a vegetarian burger.
Place the portabellos and vinaigrette in a large zip top bag. Zip and lightly rub the vinaigrette into the mushrooms. Let marinate for at least 30 minutes. Prepare the grill or a grill pan with a light layer of nonstick cooking spray. Line a plate with a layer of paper towels.
Remove the mushrooms from the bag, drain, and season with salt and pepper on both sides. Heat the grill to medium and place the mushrooms gill side down. Cook for 4 minutes, flip, and repeat on the other side for about 4 minutes more, or until the both mushrooms are almost cooked through.
Transfer the mushrooms to the paper-lined plate, gill side down. Cut each mushroom into quarters and place each quarter on the bottom half of the dinner rolls. Top each with tomato, onion, and the remaining dinner roll half and enjoy.