Prepare grill to medium heat. Season chicken breasts with desired amount of Cajun seasoning. Place chicken on grill; grill 10-12 minutes, turning occasionally, or until internal temperature reaches 170°F and juices run clear.
Brush chicken with barbecue sauce last 5 minutes of cooking. Place bacon and cheese on chicken and continue grilling until cheese is melted.
Remove from grill and place on hamburger buns. Top with lettuce, tomatoes and onions, if desired.