Slice the cucumbers: Trim ends. Use a knife, mandoline, or peeler to slice them into very thin rounds.
If using thick-skinned cucumbers, peel first and scoop out seeds to prevent excess wateriness.
Salt and rest: Place the slices in a colander and toss with the kosher salt. Let sit for 10 minutes to draw out moisture. This keeps the salad crisp and prevents a watery dressing.
Mix the dressing: In a small bowl, whisk rice vinegar, soy sauce, sugar, and sesame oil until the sugar dissolves.
Taste and adjust sweetness or saltiness as needed.
Pat dry: Rinse the cucumbers lightly to remove excess salt, then pat them dry with paper towels. Don’t skip drying—too much moisture will dilute the dressing.
Toss it together: In a medium bowl, combine cucumbers, scallion, sesame seeds, and any optional add-ins. Pour over the dressing and toss gently to coat.
Chill briefly: Let the salad rest in the fridge for 5–10 minutes so the flavors meld.
Give it a quick toss before serving.
Serve: Taste once more and finish with a sprinkle of sesame seeds or a pinch of heat if you like. Serve cold.