Step 1: Boil a large pot of salted water and cook the elbow macaroni according to package directions until slightly under al dente. Drain and set aside.
Step 2: In a small bowl, toss the shredded chicken with the buffalo wing sauce until fully coated and set aside.
Step 3: In a large saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1-2 minutes until bubbling and pale gold to create a roux.
Step 4: Gradually whisk in the milk, ensuring no lumps remain. Continue cooking and whisking until the sauce thickens enough to coat the back of a spoon.
Step 5: Remove the pan from the heat. Stir in the garlic powder, cayenne, salt, and pepper. Add the grated cheddar cheese in handfuls, stirring until completely melted and smooth.
Step 6: Fold the cooked macaroni and the buffalo chicken into the cheese sauce until every noodle is well-coated.
Step 7: Serve immediately in bowls, garnished with sliced green onions and an extra drizzle of buffalo sauce if desired.