For dressing: Combine soy sauce, rice vinegar and sesame oil in bowl.
For the salad: Prepare noodles, radishes, and cucumber, and chill in refrigerator for at least 1 hour.
To serve, add noodles to large dish, layer them with radish and cucumber pieces. Scatter with black sesame seeds. Spoon dressing over dish, garnish with fresh cilantro sprigs and serve immediately at the table to share. Make it substantial by adding cooked shrimp or chicken or cubed tofu.
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.