Put the yogurt and mustard in a large bowl. Rinse the parsley. Chop roughly. Add to the bowl. Stir to make the dressing for the slaw.
Pull any damaged outer leaves off and finely slice the cabbage. Rinse it. Pat dry. Peel the carrot. Coarsley grate it. Peel the onion. Halve it, then thinly slice it. Add the veg to the bowl. Season. Stir to coat in the yogurt dressing.
Sprinkle 1 tbsp of the flour on a plate and season well with salt and pepper. Break the egg into a shallow plate and lightly beat. Sprinkle the breadcrumbs on a separate plate.
Press a chicken fillet down with your palm. Slice into the side with a sharp knife. Don’t cut all the way to the other side. Open out like a butterfly. Repeat with the other fillet. Cover them with cling film. Bash them flat so they’re about ½ cm thick.
Take a butterflied chicken fillet and dip both sides in the seasoned flour to coat. Then dip it in the beaten egg. Sit the fillet on the breadcrumbs and turn to coat. Repeat with the second fillet. Put to one side.
Just before you fry the chicken, wash the apple and coarsely grate it – you don’t need to peel it, just grate down to the core. Add to the slaw. Stir.
Heat 2 tbsp oil in a frying pan. When hot, add a breaded chicken fillet. Fry for 2-3 mins on each side till crisp and golden, turning with tongs. Pop on a warm serving plate and repeat with the other fillet. Serve with the slaw.