In a heavy bottomed pot over medium heat, melt the butter Reduce the heat to low and whisk in the flour to make a roux, cook for 4 minutes, stirring constantly to prevent scorching.
Pour 1 cup of milk into the roux, whisking constantly as the sauce thickens. Add the rest of the milk, in 1/2 cup portions, add the hot sauce and salt whisking constantly to prevent lumps. Simmer the sauce over low heat for 8 minutes, stirring the bottom of the pot with a spatula to prevent burning.
Cook macaroni, drain and set aside.
In a 13X9" baking pan, spray with nonstick spray. pour small amount of bechamel in the bottom of the pan with a little of the cheese. Sprinkle the chicken with the onion powder, and chipotle sauce, place half of the chicken in the pan then top with half of the peppers. Now add half of the macaroni, salt and pepper to taste, pour half of the bechamel sauce over the macaroni and half of the cheese. Repeat ending with the cheese.
Bake at 350°F for about 20 minutes. Makes 6 large servings.