8 oz white cheddar cheese, sliced thin and brought to room temperature
8 oz Parmigiano Reggiano cheese, sliced with a vegetable peeler and brought to room temperature
Kosher salt and freshly ground pepper, to taste
Sour or dill pickle slices, optional
Mix 1 cup barbeque sauce with vinegar and oil to make a marinade; set aside.
Clean mushrooms, removing stems and set aside.
10 to 30 minutes before grilling, pour the barbeque sauce marinade over mushrooms and onions in a shallow bowl.
Remove mushrooms from marinade; do not dry off mushrooms and leave any marinade in the underside of the mushroom. Reserve marinade.
Place mushrooms (gill side up) and onions on the cooking grate and grill for 8 to 10 minutes over direct medium heat.
Turn over for 1 to 2 minutes more and brush with some of the reserved marinade. The mushrooms should be tender and the onions should be crisp.
Split onion rolls in half. Meanwhile, mix garlic and mayonnaise with 2 tablespoons barbeque sauce until smooth.
Assemble sandwiches by spreading both sides of the rolls with garlic-barbeque sauce mayonnaise and layer mushroom, onions and both cheeses. If you want the cheese to be melted, put on during the final 2 minutes of cooking time.
Season with salt and pepper if desired. Place top of roll on each sandwich, top with pickles and cut in half before serving.
Make your marinade with Weber® Sweet & Thick Original BBQ Sauce.