Preheat the oven. Heat to 425°F (220°C).
If you have a pizza stone, place it in the oven to preheat. A hot surface helps the flatbread crisp up nicely.
Prep the chicken. Toss the cooked chicken with 1/3 to 1/2 cup BBQ sauce until lightly coated. You want it saucy, not drenched.
Set aside.
Make the garlic-parmesan base. In a small skillet over medium heat, warm 1 tablespoon olive oil or melt 1 tablespoon butter. Add the minced garlic and cook 30–45 seconds until fragrant. Stir in the cream and bring to a gentle simmer.
Add 1/2 cup grated Parmesan, a pinch of salt, and black pepper. Stir until smooth and slightly thickened, 1–2 minutes. Remove from heat.
Prep the flatbread. Place the flatbread on a parchment-lined sheet or preheated stone.
Lightly brush the edges with olive oil for a golden finish.
Spread the base. Spoon the warm garlic-parmesan sauce over the flatbread, leaving a small border. This creates a rich, savory layer that complements the BBQ flavor.
Add the cheeses. Sprinkle a thin layer of mozzarella over the sauce. This helps the toppings adhere and gives a gooey center.
Top with chicken and extras. Scatter the BBQ chicken evenly.
Add thin slices of red onion if you like a sharper bite. Finish with the remaining mozzarella and a light dusting of Parmesan.
Bake. Slide into the oven and bake 10–14 minutes, until the cheese is melted and bubbly and the edges are golden-brown. If using a stone, check at 9–10 minutes since it runs hotter.
Finish and garnish. Remove from the oven.
Drizzle a small ribbon of BBQ sauce over the top. Sprinkle chopped parsley or cilantro, a pinch of red pepper flakes if you want heat, and a quick squeeze of lemon to brighten the flavors.
Slice and serve. Let it rest 2–3 minutes so the cheese settles, then cut into squares or wedges. Serve hot.