Prep the cucumbers: Slice cucumbers as thinly as you can. A mandoline makes this easy. Toss slices with 1 teaspoon kosher salt and let sit 10 minutes to draw out water.
Soak the wakame: Place dried wakame in a bowl, cover with cool water, and soak 5–10 minutes until soft. Drain well and squeeze out excess water. If pieces feel large, chop into bite-size strips.
Make the dressing: In a small bowl, whisk rice vinegar, sugar, soy sauce, mirin (if using), and a pinch of salt until the sugar dissolves. Taste and adjust sweetness or acidity.
Remove cucumber moisture: Rinse the salted cucumbers briefly to remove excess salt, then squeeze gently by handfuls to remove as much water as possible. This step keeps the salad crisp and prevents dilution.
Toss and finish: Combine cucumbers and wakame in a bowl. Pour over dressing and toss to coat. Sprinkle with toasted sesame seeds and any optional garnishes. Serve immediately or chill 10–20 minutes for extra refreshment.
Flavor tip: A few drops of sesame oil add aroma but can overwhelm—use sparingly.
Texture tip: Salting and squeezing the cucumbers is the secret to a crunchy, non-watery salad.
