Wash the cucumbers, cut them in half lengthwise, then slice into thin half-moons.

Place cucumber slices in a bowl and sprinkle with salt. Let sit for about 15 minutes to draw out excess water.

After 15 minutes, add thinly sliced red onion to the cucumbers.

In a separate bowl, mix together vinegar, olive oil, sugar, and black pepper. Stir until the sugar is dissolved.

Drain any liquid from the cucumbers and onions, then pour the dressing over the mixture. Toss to coat well.

Let the salad sit in the refrigerator for at least 30 minutes to let the flavors meld.