Preheat your oven to 400°F (200°C). Place a baking sheet in the oven to heat up.
In a bowl, combine the shredded chicken with the BBQ sauce, garlic powder, onion powder, salt, and pepper. Mix well until the chicken is evenly coated.
Once the oven is preheated, carefully remove the hot baking sheet. If desired, lightly brush it with olive oil to prevent sticking. Place the flatbread on the hot sheet.
Spread the BBQ chicken mixture evenly over the flatbread, making sure to leave a small border around the edges. Sprinkle the mozzarella and cheddar cheese generously over the top. Add the thinly sliced red onion on top of the cheese for a bit of crunch and flavor.
Place the assembled flatbread back in the oven and bake for about 10-12 minutes or until the cheese is melted, bubbly, and just starting to turn golden.
Remove the flatbread from the oven and let it cool for a minute. Sprinkle fresh chopped cilantro over the top for a nice burst of flavor and color. Slice into wedges and serve warm.