Preheat your oven to 350°F (175°C).
Cook the elbow macaroni in a large pot of salted boiling water according to package instructions until al dente. Drain and set aside.
In a large skillet, melt the butter over medium heat. Add the shredded chicken and buffalo sauce, stirring to combine. Cook for about 5 minutes until heated through.
In a saucepan, combine the milk, cream cheese, garlic powder, onion powder, salt, and pepper. Whisk over medium heat until the cream cheese is completely melted and the mixture is smooth.
Stir in 2 cups of the shredded cheddar cheese into the sauce, continuing to whisk until melted and creamy.
In a large mixing bowl, combine the cooked macaroni, the buffalo chicken mixture, and the cheese sauce. Mix until well combined.
Pour the mixture into a greased 3-quart baking dish. Sprinkle the remaining shredded cheddar cheese and breadcrumbs evenly over the top.
Bake in the preheated oven for 20-25 minutes, or until bubbly and golden brown on top.
Remove from the oven and let cool for a few minutes. Garnish with chopped green onions if desired before serving.