Drain the cellophane noodles and cut them into 3- to 4-inch lengths and set aside.
In a soup pot, bring the vegetable stock to a boil and add the carrots, garlic, soy sauce, rice vinegar, and ginger. Lower the heat and simmer, uncovered, for about 5 minutes.
In a separate pot, bring about a quart of water to a boil. Meanwhile, stir the zucchini and the bok choy into the simmering vegetable stock and cook for 4 minutes, until the vegetables are just tender.
In a bowl, mash the miso with 3 tablespoons of the hot soup broth to make a thick sauce and return it to the soup. Add the sesame oil.
When the water is boiling, add the soaked cellophane noodles into the pot and cook for 2 or 3 minutes, until just tender, and drain.
To serve, evenly divide the noodles among the soup bowls, ladle the soup over the noodles, and garnish with sesame seeds and scallions.