Cut the chicken into 1 inch pieces. Place them in a medium bowl and add buttermilk. Soak the chicken in buttermilk for at least 1 hour.
In a small bowl, combine the cornstarch, salt, pepper, onion powder, garlic powder, smoked paprika, and cayenne pepper.
Use a slotted spoon to remove the chicken from the buttermilk (*reserve buttermilk). Transfer the chicken to a gallon sized ziplock bag and sprinkle the cornstarch mixture over it. Seal the bag and shake to coat.
Use a fork to remove chicken one piece at a time from the cornstarch mixture. Briefly re-dip in the buttermilk, then coat with panko bread crumbs.
Heat oil in a medium skillet over medium heat to 350°. Add breaded chicken in batches and fry about 1 1/2 - 2 minutes on each side, until golden brown. (*Be sure the oil doesn't get too hot or the breading will over-brown before the chicken cooks all the way through.) Remove from the oil using a spider strainer; place on a large plate lined with paper towels.