Preheat oven to 450 degrees F. Place bread shell on a baking sheet, bottom side up. Coat bread shell with nonstick cooking spray. With a pizza cutter, cut bread in half. Sprinkle cheese evenly over bread halves. In a small bowl combine chicken and barbecue sauce. Top one bread half with chicken mixture and the bacon slices.
Bake for 7 to 9 minutes or until cheese melts and bacon is crisp. Cool on baking sheet for 2 minutes. Meanwhile, in a small bowl combine lettuce, onion, and ranch salad dressing.
To serve, cut each half into quarters to make eight wedges. Spoon lettuce mixture evenly over wedges with chicken. Top with tomato slices. Invert remaining wedges over toppings.