The shortest recipe on this site, and one of the best things on it.
Drain the crab properly. Tip it into the lid, press it, pour the brine away, press again. That brine is the entire reason tinned crab has a reputation, and thirty seconds removes it.
Then: crab in a bowl, lemon juice, olive oil, a lot of black pepper, a pinch of chilli. Turn it over gently: three or four turns, no more, or you shred it. Pile onto oatcakes.
That is the recipe. Resist adding anything else; this is the one dish in the cupboard where restraint is the technique.
Serves 2 as a starter or a light lunch. It does not keep: dress it when you are ready to eat it.