Half-peel the cucumber in alternating stripes.
Cut it in half lengthways, then cut each half in half again lengthways, so you can easily scoop out the seeds with a teaspoon.
Put the lengths of cucumber on a board, flesh side down, then use the flat of a cleaver (or a rolling pin or other heavy object) to bash along their length to bruise, rather than pulverise.
Cut into slices about 1cm wide and on a slight diagonal, then put these in a bowl.
Whisk the garlic, vinegar and soy sauce into the sesame paste until smooth.
Taste and adjust the seasoning as necessary (add a pinch of sugar, if you like), then pour over the cucumber and toss.
Just before serving, drizzle over the chilli oil and sediment, if using.
