Preheat your oven to 350°F (175°C).
Cook the elbow macaroni according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the cooked macaroni, shredded chicken, buffalo sauce, garlic powder, onion powder, and black pepper. Mix well.
In a separate bowl, combine the cream cheese and milk, stirring until smooth. Add this mixture to the macaroni and chicken, and mix until everything is well combined.
Stir in the shredded cheddar and mozzarella cheeses, reserving a small amount of each for topping.
Transfer the mixture to a greased 9x13-inch baking dish. Sprinkle the reserved cheeses on top.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes. Garnish with chopped green onions and blue cheese crumbles, if desired.