Prep Time: 10
Cook Time: 10
Serves: Serves: 4
Prepare grill or preheat broiler.
Trim off mushroom stems. Use a spoon to scoop out and discard mushroom gills from undersides of mushroom caps. Brush dressing over tops of mushrooms and over both sides of onion slices.
Grill mushrooms and onion slices over medium heat on a covered grill or broil 4 inches from heat source 5 minutes per side or until vegetables are tender. Place cheese over mushrooms and place cut sides of rolls down on grill or up on broiler pan; continue grilling or broiling 1 minute or until cheese is melted and rolls are lightly toasted.
Combine mayonnaise and mustard; spread over tops of rolls. Place lettuce and tomato over bottom of rolls. Place mushrooms and onions over tomatoes; close sandwiches with roll tops.