Heat oven to 400. Spray broiler pan with nonstick cooking spray. In a shallow bowl, combine buttermilk and 1 tablespoon of the taco seasoning mix; mix well.
In another shallow bowl, combine remaining taco-seasoning mix, breadcrumbs, flour, salt and pepper, mix well.
Dip chicken pieces in buttermilk mixture; coat with breadcrumb mixture. Place on sprayed broiler pan. Let stand 10 minutes. Drizzle chicken with butter. Bake 45 - 55 minutes or until chicken is fork tender and juices run clear.