Place chicken breasts, one at a time, into a plastic bag. Flatten using a rolling pin or meat hammer until they are uniformly 1/2 - 3/4 inch thick. Repeat until each breast is pounded out. Cut breasts into palm-sized pieces.
Mix together 1/2 cup flour, panko, salt, garlic powder, seasoning salt, cayenne, and onion powder. Set aside. In separate bowl, mix egg and milk. In another bowl, place 1/2 cup flour with a few shakes of salt and pepper. Mix well.
Using a fork, dunk each piece of chicken first in the flour, then into the egg wash, and finally coat with the panko mixture. Make sure in each step the breast is coated completely. Fry over medium to medium high heat in preheated oil until golden brown on both sides and inside is no longer pink, approximately 6-7 minutes depending on your stove.
Remove from oil and let sit for 3-4 minutes on a wire rack before serving.