Marinate your mackerel fillet in a warm rice vinegar, thinly sliced shallot, sliced carrot, caster sugar, peppercorn broth. 

Make a watercress purée 

Thinly slice the radish, put in ice cold water

Horseradish cream ( grated fresh horseradish with double cream, bring to the boil and leave to infused before passing through the strain), place in a small squeezy bottle.

20 Minutes top job. Delicious, fresh and an awesome way to use mackerel.