Wash the cucumbers thoroughly. Peel them in alternating strips, creating a striped pattern. Slice the cucumbers thinly (about ⅛-inch thick).
Place the cucumber slices in a colander set over a bowl. Sprinkle with the salt, toss gently to coat, and let sit for 30 minutes. After 30 minutes, gently press the cucumbers with paper towels to remove additional moisture.
While the cucumbers are draining, slice your red onion as thinly as possible. For a milder flavor, soak the slices in ice water for 10 minutes, then drain well.
In a medium bowl, whisk together the sour cream, vinegar, sugar, pepper, and garlic (if using) until smooth and well combined. Taste and adjust seasonings.
In a large serving bowl, combine the drained cucumbers, onion slices, and fresh dill. Pour the dressing over the vegetables and gently toss until everything is evenly coated.
Cover the bowl and refrigerate for at least 30 minutes, though 2 hours will yield the most flavorful results.