Slice the cucumbers and carrots thinly using a knife or mandoline, and place them in a large mixing bowl.
In a small bowl, whisk together the sesame oil, rice vinegar, soy sauce, sugar, and salt until well combined.
Pour the dressing over the sliced vegetables and toss gently to coat everything evenly.
Sprinkle the toasted sesame seeds and green onions over the salad, and toss once more.
Let the salad sit at room temperature for about 10 minutes to allow the flavors to meld and the vegetables to soften slightly.
Garnish with fresh cilantro leaves if desired, then serve immediately or chill briefly before serving.