1 tablespoon unseasoned rice vinegar
2 teaspoons toasted sesame oil
1 teaspoon toasted sesame seeds
1/4 teaspoon crushed red pepper flakes
1 bunch cilantro leaves with tender stems, cut into 2 inches pieces
4 celery stalks, thinly sliced on a diagonal
2 small cucumbers or 1/2 large, thinly sliced
6 scallions, thinly sliced on a diagonal
Kosher salt, freshly ground pepper
Whisk vinegar, oil, sesame seeds, and red pepper flakes in a large bowl. Add cilantro, celery, cucumbers, and scallions. Season with salt and pepper and toss to combine.
DO AHEAD: Salad can be made 6 hours ahead. Cover and chill.