Keep the cucumbers crunchy by draining the slices in advance. This will also prevent too much water from seeping into the creamy labneh dressing; a little of this may still happen, but just give the salad a quick stir before serving, cold. Low-fat or non-fat labneh or Greek yogurt can be used here; add a squeeze of lemon juice to the salad before serving to boost flavor.
Cut the cucumbers lengthwise, then in 1/4-inch slices. Place them in a colander and sprinkle them with the kosher salt, stirring to coat them well. Drain for 30 minutes, stirring occasionally.
Lay the cucumber slices on paper towels in a single layer, then lay paper towels over top and press to soak up the liquid.
In a medium bowl or serving dish, stir the labneh, chopped herbs, pepper and dried mint. Add the cucumbers and onion, and stir well to coat the cucumbers with the labneh.
Chill for at least one hour and up to one day. Stir before serving, cold.