COMBINE dressing and mayo; pour into large resealable plastic bag. Add chicken; seal bag. Turn bag over several times to evenly coat chicken with the dressing mixture. Refrigerate at least 20 min. or up to 2 hours to marinate.
PREHEAT grill to medium-high heat. Remove chicken from marinade; discard bag and marinade. Thread chicken and onions alternately onto 16 wooden skewers.
GRILL 8 to 10 min. or until chicken is cooked through, turning occasionally. Meanwhile, place lemon, cut-sides down, on grill grate next to kabobs. Squeeze lemon juice over kabobs just before serving.