Preheat your oven to 350°F (175°C) and cook the elbow macaroni in boiling salted water until al dente, about 7-8 minutes. Drain and set aside.

In a medium saucepan, melt 4 tablespoons of unsalted butter and whisk in 1/4 cup of all-purpose flour to form a roux, about 1 minute.

Gradually add 3 cups of milk to the roux, whisking constantly until it thickens, about 4-5 minutes.

Stir in 2 cups of shredded cheddar cheese and 1 cup of shredded mozzarella cheese until melted and smooth.

Add 1 teaspoon of garlic powder, 1 teaspoon of onion powder, and season with salt and pepper. Stir to combine.

Fold in the cooked macaroni and 2 cups of shredded BBQ chicken until well combined.

Transfer the mixture to a greased 9x13 inch baking dish and sprinkle with breadcrumbs if desired.

Bake for 20-25 minutes until golden brown on top and bubbly.

Let it rest for 10 minutes, garnish with green onions and parsley, and serve warm.