01 - Set oven to 475°F and position a pizza stone inside if using.
02 - Bring a medium pot of salted water to a boil. Add macaroni and cook until just al dente, about 6 to 7 minutes. Drain and set aside.
03 - Melt butter in a saucepan over medium heat. Whisk in flour, cook for 1 minute, then gradually add milk, whisking constantly until smooth and thick, about 2 to 3 minutes.
04 - Remove from heat and stir in cheddar cheese until fully melted. Season with salt and pepper. Gently fold in cooked macaroni and set aside.
05 - In a bowl, toss shredded chicken with BBQ sauce until evenly coated.
06 - On a lightly floured surface, stretch or roll dough into a 12-inch round. Transfer to a parchment-lined baking sheet or hot pizza stone.
07 - Spread prepared mac and cheese evenly over the dough, leaving a 1/2-inch border along the edges.
08 - Scatter BBQ chicken over mac and cheese. Sprinkle mozzarella on top and distribute red onion slices evenly.
09 - Place pizza in the oven and bake for 12 to 15 minutes, until crust is golden and cheese is bubbly and beginning to brown.
10 - Remove pizza from oven. Drizzle with extra BBQ sauce and sprinkle with cilantro, if desired. Slice and serve hot.