Peel and finely chop the onion. Mix minced meat, breadcrumbs, egg and soy sauce, season with salt and pepper. Form about 20 small balls from the minced meat. Wash and clean the zucchini and cut them into sticks.
Wash and clean the celery and cut into small slices.
Cook the pasta in boiling water for about 4 minutes. Bring dashi stock to the boil, add zucchini, celery and meatballs, cook for about 10 minutes. Mix miso paste with some hot broth until smooth and add to the broth.
Wash the chives, shake dry and cut into fine rolls. Add the noodles to the stock and serve in bowls. Sprinkle the chives over the pasta.