Tip the oats on to a plate and season them with salt and pepper, then stir in the chopped parsley.
Dip each fish fillet into the beaten egg and then coat with the porridge oats.
Heat the butter and oil in a large frying pan and when hot, add the mackerel to the pan, cooking for 2-3 mins on each side, or until crisp all over.
Remove the mackerel fillets from the pan and drain them on absorbent kitchen paper. Serve immediately with lemon wedges to squeeze the juice over the fish.