Heat oil in a medium soup pot and sauté the onions for 1 to 2 minutes. Add all remaining ingredients except for the green beans, miso and scallions. Cover and bring to a boil. Reduce the flame to medium-low and simmer for 10 minutes. Add green beans and cook another 2 minutes. Reduce the flame to low, add the pureed miso, and simmer uncovered for another 1 to 2 minutes. Serve garnished with scallions.
Per serving - 112 calories, 4 gram fat (18% calories from fat), 7 gram protein, 33 gram carbohydrate, 7 gram fiber, 0 milligram cholesterol, 249 milligram sodium