Prepare the Cucumber Ribbons: Using a vegetable peeler or the thinnest setting on a mandoline, slice the unpeeled cucumbers lengthwise into long ribbons.
Sweat the Cucumbers: Place the cucumber ribbons into a large mesh sieve and set it in the sink. Sprinkle evenly with 1 ½ teaspoons of flaky sea salt and toss gently. Let the ribbons stand for 25 minutes to draw out all the excess water.
Make the Dressing: While the cucumbers are resting, combine the Greek yogurt, extra-virgin olive oil, and apple cider vinegar in a wide serving bowl. Whisk until the mixture is smooth and creamy.
Add Aromatics: Stir the minced red onion, fresh chives, parsley, lemon juice, lemon zest, and garlic powder into the dressing.
Dry and Combine: Gently squeeze the cucumber ribbons to expel any remaining water, then place them on a layer of kitchen towels and pat thoroughly dry. Transfer the dried ribbons to the bowl with the dressing.
Toss and Season: Using tongs, gently fold the cucumber ribbons into the dressing until they are evenly coated. Season with a pinch of white pepper. Taste the salad and add more salt only if necessary, as the cucumbers will have retained some saltiness.
Chill and Serve: Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld and the salad to chill completely before serving.
