Brush both sides of mushrooms evenly with 3 tablespoons of the salad dressing.
Coat a grill rack with cooking spray.
Place mushrooms on rack; grill, covered, 5 minutes on each side or until tender.
Place cheese over mushrooms and grill 1 minute longer or until cheese has melted.
Brush buns with remaining dressing and grill until lightly toasted.
Place mushrooms over bottoms of buns, top with roasted red pepper pieces and tops of buns.