Wipe the mushrooms with a damp kitchen towel. Cut their rubbery stems off. In a large mixing bowl, mix balsamic vinegar, mashed garlic, olive oil, salt, and parsley well. Coat each mushroom with the marinade and leave them in the bowl. Let them sit for 5 min
Thread them on skewers and grill them for 5-7 minutes per side or until golden brown.
