Place water, kombu and shiitake in a medium soup pot, cover and bring to a boil. Reduce the flame to medium-low and simmer 4 minutes. Remove the kombu and set aside for future use or discard. Cover and simmer the shiitake for another 10 minutes.
While the shiitake are simmering, soak the mekabu in hot water to cover for 10 minutes, drain and soak in cold water for 2 more minutes. Drain mekabu.
Remove the shiitake. Discard the stems and slice the shiitake. Place slices in the pot. Add the crumbled bonito flakes, cauliflower and carrots. Cover and simmer 2 minutes. Reduce the flame to low. Puree the miso with a little soup broth and add miso to the pot. Stir to mix. Simmer without boiling for 2 minutes. Turn the flame off, add the mekabu and the scallions and serve.
Per serving - 62 calories, 1 g fat (11% calories from fat), 4 g protein, 11 g carbohydrate, 5 g fiber, 0 mg cholesterol, 693 mg sodium