Remove any excess moisture on the chicken breasts with a paper towel.
Butterfly the chicken breasts. Pound the chicken to an even thickness of about 1cm. Season both sides with salt & pepper.
In a large skillet, heat up the oil until it reaches to 340ºF (170ºC).
Coat the chicken breasts in flour, and dust off any excess flour. Then coat it with the beaten egg. Lastly, coat it with the panko breadcrumbs, while packing the panko into the chicken tightly - make sure there are no empty spots.
Gently place the breaded chicken into the oil, frying for about 3 minutes, while turning the chicken once halfway through. Deep fry until both sides are golden brown. Let it rest on a wire rack for a few minutes.