Preheat oven to 350. Prepare a 11"x7" casserole dish with cooking spray; set aside. In a large sauce pan, cook chicken and onions until chicken is no longer pink. Stir in tomato sauce and spaghetti sauce mix. Mix well and cook over medium heat until mixture begins to thicken. Meanwhile, in another saucepan, heat evaporated milk and cream cheese . Cook until smooth. Stir in cooked noodles. Pour noodle mixture onto bottom of prepared pan. Spread chicken mixture over top. Sprinkle mozzarella cheese over top. Bake for 20 minutes, or until heated through.