PREHEAT grill to medium heat. Place mushrooms, cap-sides up, on grate of grill. Brush with about half of the dressing; grill 6 min.
TURN mushrooms over. Add tomatoes to the grill. Cook 3 to 5 min. or until mushrooms are tender and tomatoes are heated through, turning tomatoes after 3 min.
SPREAD cut sides of rolls with pesto. Fill evenly with mushrooms, tomatoes and 2% Milk Singles.