HEAT grill to medium heat.
COMBINE barbecue sauce and dressing. Add 1/4 cup to peanut butter in small bowl; mix well.
GRILL chicken 5 to 7 min. on each side or until done (165ºF), brushing occasionally with remaining barbecue sauce mixture for the last few minutes. Meanwhile, grill peppers and onions 4 to 5 min. or until crisp-tender, and grill tomatoes 2 to 3 min. or until tender, turning once.
CUT chicken and vegetables into thin strips; place on tortillas. Roll up tightly. Serve with peanut butter mixture.