For the dressing: Combine the soy sauce, rice vinegar and sesame oil in a bowl.
For the salad: Prepare the noodles, radishes, and cucumber, and chill them in the refrigerator for at least 1 hour.
To serve, add the noodles to a large dish, layer them with some radish and cucumber pieces and scatter over the black sesame seeds. Spoon the dressing over the dish, garnish with some fresh cilantro sprigs and serve immediately at the table to share. You could also dish up individual portions.
Try two other dressings to enhance this dish.
Combine the chiles, soy sauce, rice vinegar, sesame oil, ginger, and chopped cilantro in a small bowl. Combine the hot chile sauce and soy sauce in a small bowl.