Preheat oven to 350 F. Spray a small casserole dish with nonstick cooking spray. Rinse the quinoa thoroughly and cook according to package directions. Meanwhile, add the butter to a medium saucepan and set over low heat. Let the butter melt, then add the flour. Cook for about 2 minutes, whisking constantly. Gradually add the milk to the pan, continuing to whisk so you don't wind up with lumps. Increase the heat to medium, and cook, whisking frequently, until the sauce thickens. Remove the pan from the heat then add the cheddar cheese and buffalo sauce. Whisk until the cheese is completely melted and the sauce is smooth. Add the cooked quinoa and chicken and stir until incorporated. Transfer the mixture to the baking dish (or dishes, if you're using individual ones). Sprinkle with cheese. Bake for 15-20 minutes, or until the sauce bubbles around the edges of the dish.