is this fresh mackerel or smoked? if fresh, skin and fry the fillets really slowly, the oil should hardly bubble, more like poaching really, until just cooked.
drain and flake the meat, let it cool and mash with a fork with black pepper and a dash of horseradish sauce. i add a dash of soy to mine. you can use chilli sauce instead of horseradish if u like.
bay leaves, chives or parsley can be added too