In a shallow dish, coat the steak with the hoisin sauce and some black pepper. Leave to marinate while you make the noodle cake.
Mix all the ingredients (apart from the oil) for the noodle cake with some black pepper in a medium-sized bowl. Heat half the oil in a medium-sized, non-stick frying pan (or omelette pan). Tip in the eggy mixture and cook over a medium heat for about 3-4 mins until golden. Turn over – the easiest way is to put a flat plate on top of the frying pan – invert to release the cake, then slide back in. Cook for another 3-4 mins, then slide out and keep warm in a low oven while you cook the steak.
Give the pan a quick wipe and heat the rest of the oil. Cook the steak for about 2-3 mins each side (depending on the thickness of your steak) for medium-rare, or longer for well done. Rest for a couple of mins, then serve in slices, scattered with the mint and radish, with the noodle cake.