Run a fork down the length of the cucumbers to create grooves all over the surface, then thinly slice into rounds using a speed peeler, mandolin (use the guard!) or a very sharp knife and patience. Place in a colander set over a bowl, toss with a generous pinch of sea salt, then set aside for 10 to 15 minutes to release the moisture into the bowl.
Meanwhile, roughly chop most of the dill, reserving a few nice fronds for later.
Discard the cucumber juice and transfer the cucumber to the now empty bowl. Finely grate in the zest of the lemon, squeeze in its juice, drizzle in 2 tablespoons of oil, season with black pepper and chuck in the dill. Toss everything together, then sprinkle the reserved dill fronds over the top.