For the dressing, combine all ingredients in a blender or small food processor and blitz to a smooth paste. If you don't have one, chop up the herbs, anchovies and capers as finely as possible and then whisk in the remaining ingredients.
Top and tail the green beans, and rinse in fresh water. Leave to drain, then put inside a large ziplock bag with the very thinly sliced lemon (including the pith). Season with salt and pepper. Seal the ziplock bag and use a rolling pin or something heavy to smash the beans until they’re mostly split and have broken up a bit - this makes them absorb lots of flavour from the lemon and seasoning.