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