Remove stem from mushrooms. With a table knife, scrape black gills from mushrooms. Rinse and pat dry. Place in a zip-lock bag.
Combine remaining ingredients. Whisk to combine. Pour marinade into zip-lock bag. Press to remove as much air as possible and seal, making sure that marinade is evenly distributed. Let sit at room temperature for 1 to 2 hours, turning every 15 minutes or so.
Prepare a charcoal fire on grill. Grill mushrooms, covered with grill lid, over medium-high heat four minutes on each side or until tender. Yield: 4 servings.