Prepare grill to medium heat. Place chicken on grill; grill 10-12 minutes, turning occasionally, until chicken reaches an internal temperature of 170°F and juices run clear. Brush with ¾ cup barbecue sauce last 5 minutes of grilling.
Meanwhile, combine dressing with 2 tablespoons barbecue sauce. In large bowl, toss lettuce, cheese, beans, corn, onion, tomato and avocado with dressing; salt and pepper to taste.
Divide salad among 6 dinner plates. Slice chicken and place over salads. Top with broken tortilla chips and drizzle with remaining barbecue sauce.