Slice the hanpen in half diagonally to make triangles, then slice across the middle to make a little pouch. Next stuff with cheese.
Spread out your flour and panko breadcrumbs onto plates. Dust the hanpen with the flour, then dip in the beaten egg and finally roll in the panko.
Heat a generous quantity of oil in your frying pan. Add the hanpen and fry until both sides turn a golden brown. Remove from the oil and drain on a little bit of kitchen towel, before serving and enjoy.