1. Pour 1/4 cup Wish-Bone® Italian Dressing over vegetables in large resealable plastic bag; turn to coat. Repeat with 1/4 cup Dressing and chicken. Close bags and marinate in refrigerator 30 minutes.
2. Meanwhile, whisk 1/4 cup Dressing with Mayonnaise in small bowl; set aside.
3. Remove vegetables and chicken from marinades, discarding marinades. Grill chicken and vegetables, turning once and brushing with remaining 1/4 cup Dressing, 10 minutes or until chicken is thoroughly cooked and vegetables are tender. Let stand 10 minutes. Slice chicken and red pepper.
4. Toss lettuce with 1/2 of the mayonnaise mixture, then arrange on platter. Top with vegetables and chicken. Serve salad with remaining mayonnaise mixture.