Heat oven to 400°F for dark or nonstick pan (425°F for all other pans). Spray 15x10-inch pan with sides with cooking spray.
Unroll dough in pan; starting at center, press dough into 15x10-inch rectangle. Bake about 8 minutes or until light brown.
Meanwhile, in medium bowl, place chicken and barbecue sauce. Using 2 forks, toss until chicken is coated with sauce.
Sprinkle 1 cup of the cheese over crust. Spoon and spread chicken mixture evenly over cheese. Top with red onion and remaining 1 cup of cheese. Bake about 5 minutes longer or until cheese is melted. To serve, cut into 6 rows by 3 rows. Sprinkle with parsley.