Wash hands with warm, soapy water for 20 seconds.
Preheat oven to 375℉. Spray a 9x13-inch baking pan with nonstick spray. Set pan aside.
If chicken is not cooked, cook first then cut or shred into bite-sized pieces.
If mashed potatoes are not cooked, prepare and set aside. For instant potatoes, follow package directions for cooking.
In a large saucepan over medium heat, mix together CNP Magic Mix and water or broth. Cook until smooth and thick, then remove from heat. If using butter and flour, heat butter in the pan until melted. Add flour and stir until combined into a paste. Cook until it begins to brown. Slowly whisk in water, broth, or milk and stir over medium heat until it begins to thicken.
Add chicken and vegetables.
Spread in the 9x13-inch baking pan.
Top with a layer of mashed potatoes and sprinkle with cheese, if using.
Bake for 30 minutes or until the potatoes are golden brown and the filling is bubbly.