Place chicken in a large bowl. Add the buttermilk and stir to make sure chicken is thoroughly coated. Cover and let marinate for at least 30 minutes, or up to 24 hours.

Preheat oven to 425˚. Line a baking sheet with parchment paper or aluminum foil, and coat the foil with oil spray.

Set out 3 shallow dishes for a 3-step breading station. In the first dish, combine the flour, onion powder, salt, and black pepper; mix well. In the second dish, combine the egg whites, milk, and hot sauce. Whisk together until slightly frothy. Pour Italian Panko breadcrumbs into the third dish.

Shake the excess buttermilk off the chicken, and press it into the first dish (with seasoned flour), coating both sides. Shake off the excess flour, and then dip it into the second dish (with the egg white mixture), coating all sides.

Finally, lay the chicken in the third dish, thoroughly coating all sides with panko breadcrumbs. Place the coated chicken on the prepared baking sheet, and repeat with all remaining chicken pieces. Then, liberally mist the top of each breaded chicken pieces with oil spray and bake for 25 to 35 minutes, or until browned and crispy.