Begin by bringing a large pot of salted water to a boil. Add the macaroni and cook according to the package instructions until al dente. Drain the macaroni and set it aside.
In a medium saucepan over medium heat, melt the butter. Once melted, whisk in the flour, stirring continuously for about 1 minute until it forms a roux.
Gradually pour in the milk while continuously whisking to prevent lumps. Keep stirring until the mixture thickens, about 3-5 minutes. Then, stir in the garlic powder, onion powder, salt, and pepper.
Remove the saucepan from heat and add the shredded cheddar and mozzarella cheeses. Stir until the cheeses are completely melted and the sauce is smooth.
In a separate bowl, mix the cooked shredded chicken with the BBQ sauce until evenly coated.
In a large mixing bowl, combine the cooked macaroni, cheese sauce, and BBQ chicken mixture. Stir until everything is well combined.
Preheat your oven to 350°F (175°C). Transfer the mac and cheese mixture into a greased baking dish. If you like a crunchy topping, sprinkle breadcrumbs evenly over the top.
Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the top is golden and bubbly.