Soak the shiitake mushrooms in one cup of hot water, set aside (save that water!). Heat a large soup pot over medium high heat on your stovetop, add the oil and sauté the onion until just soft, then add the kabocha squash. Continue stirring until the kabocha is just starting to heat through, then add the water and packet of dashi. Turn the heat to high so the water can come to a boil then add the brown rice, edamame, and shiitake mushrooms with its water.
Turn down the heat and continue cooking at a gentle simmer until the kabocha is soft enough to pierce with a fork. Add the miso, shoyu, mirin and fish sauce, if using (the fish sauce will add another layer of flavor to this soup – a rich umame flavor). Season with salt and pepper to taste, then ladle into serving bowls. Garnish with scallion and serve with bread for a complete meal!