In a large pot, cook the elbow macaroni according to package instructions until al dente. Drain and set aside.
In a saucepan over medium heat, melt the butter. Sprinkle the flour over the melted butter and whisk to combine, cooking for about 1 minute until it turns a light golden color.
Gradually pour in the milk, whisking continuously until the mixture thickens (about 3-5 minutes).
Stir in the garlic powder, onion powder, and season with salt and pepper.
Reduce the heat to low and add the cheddar and mozzarella cheese, stirring until completely melted and creamy.
In a large mixing bowl, combine the cooked macaroni, shredded chicken, BBQ sauce, and cheese sauce, stirring until evenly coated.
Transfer the mixture to a greased baking dish (about 9x13 inches).
Sprinkle breadcrumbs evenly over the top for a crunchy topping.
Bake in the preheated oven for 25-30 minutes, or until bubbling and golden on top.
Remove from the oven and let it cool for a few minutes. Garnish with fresh parsley before serving.