Grill vegetables 5 to 7 min or until crisp-tender, turning and brushing occasionally with dressing. Meanwhile, grill rolls, cut-sides down, 1 to 2 min. or until lightly toasted.
Remove vegetables and rolls from grill.
Cut mushrooms into thin strips. Separate onions into rings.
Spread rolls with reduced-fat cream cheese; fill with grilled vegetables, tomatoes and 2% Milk Singles.