Heat oven to 400°F. Spray a 15x10 baking dish with nonstick cooking spray. In a shallow bowl or plate combine the milk, salt and chili powder. Mix well. Place cornflake crumbs in another bowl. Dip chicken in milk mixture and then coat with cornflake crumbs. Place in baking dish on one side. In a large bowl, combine the potatoes and onion. Sprinkle with bread crumbs and paprika. Toss to evenly coat. Place in other end of baking dish and drizzle melted margarine over them. Bake at 400°F for 40-50 minutes until chicken is cooked and potatoes are tender. Stir the potatoes at the halfway mark.