In a medium soup pot or dutch oven, combine water with the shiitake mushrooms and seaweed soup mix. Bring to a boil and simmer, partially covered while you prepare the vegetables.
Prepare the vegetables and set each one aside in a small bowl as you cut it. Heat oil in large frying pan over medium- low heat. Sauté the onion with the thyme until translucent (about 5 minutes).
Add root vegetables to onion/thyme mixture and sauté another 5 minutes, stirring occasionally.
Remove the shiitake mushrooms from the simmering seaweed stock with a slotted spoon and slice on a cutting board. Discard stems. Carefully pour vegetables into the pot of soup. Season very lightly with shoyu and simmer 10 minutes more. Serve garnished with parsley and scallions.
Variation: add cut corn and sweet red bell pepper. Add a light sweet summer chickpea miso at the end.