Preheat oven to 425 degrees F and line a baking sheet with parchment paper.
Place the flatbread onto the baking sheet. Top with ½ cup barbecue sauce, keeping it about ¼" from the edge of the flatbread.
Add cheese on top of the barbecue sauce, followed by chicken and onions.
Bake for 7-9 minutes or until cheese is melted. Remove from oven and slice into 7 pieces.
Place remaining tablespoon of barbecue sauce into a resealable sandwich bag and seal shut. Snip the corner of the bag and drizzle the barbecue sauce on top of the flatbread.