Preheat your oven to 425°F and line a large baking sheet with parchment paper.
Make the BBQ sauce by combining ketchup, apple cider vinegar, brown sugar, smoked paprika, garlic powder, onion powder, black pepper, cayenne, and Worcestershire sauce in a small saucepan over medium-low heat. Stir and simmer for 5 minutes until slightly thickened. Remove from heat.
Prep the flatbreads by brushing each one lightly with olive oil, then spreading 2–3 tablespoons of BBQ sauce evenly across the surface, leaving a small border around the edges.
Add the toppings — layer on the shredded chicken, mozzarella, smoked gouda, and sliced red onion.
Bake for 10–12 minutes, until the cheese is bubbling and the edges of the flatbread are golden and crispy.
Finish and serve — pull from the oven, scatter fresh cilantro on top, and slice into pieces. Add an extra drizzle of BBQ sauce if you like things saucy.