Cook the elbow macaroni in a large pot of salted boiling water according to package instructions until al dente, about 7-8 minutes. Drain and set aside.

If using raw chicken, cook it in a skillet over medium heat until fully cooked, about 10-15 minutes. Shred the chicken and mix it with the buffalo sauce in a bowl.

In the same pot used for the pasta, melt the unsalted butter over medium heat. Whisk in the all-purpose flour and cook for about a minute, stirring constantly.

Gradually pour in the milk while whisking to prevent lumps. Stir until the mixture thickens and bubbles, about 5-7 minutes.

Remove from heat and stir in the shredded cheddar and mozzarella cheeses until melted and smooth. Add garlic powder, onion powder, and season with salt and pepper to taste.

Combine the buffalo chicken mixture with the cheese sauce, then add the cooked macaroni and mix until fully coated.

Preheat the oven to 350°F (175°C). Transfer the mixture to a greased baking dish and sprinkle extra cheese on top if desired. Bake for about 20 minutes until golden and bubbly.

Let cool for a few minutes before serving. Garnish with chopped green onions.