Buffalo Chicken Mac and Cheese

Name: Buffalo Chicken Mac and Cheese
Ingredients: 4 cups chopped cooked chicken breasts grilled, rotisserie, etc; 16 ounces box dry macaroni pasta cooked to package directions and drained; 3 1/2 cups milk; 1 1/2 cups shredded sharp cheddar cheese; 1 1/2 cups shredded Monterey jack cheese; 1/2 cup Frank's Red Hot sauce; 1/4 cup salted butter; 1/4 cup AP flour; 1/2 tablespoon spicy brown mustard; 1/2 teaspoon salt more or less to taste; 1/4 teaspoon black pepper; Chopped green onions optional