Steam beans 12 minutes or until crisp-tender, OR cook in boiling salted water 3 to 5 minutes until crisp-tender. Drain and plunge into iced water to cool 10 minutes. Drain again and pat dry. To cut the beans, fit a food processor with slicing blade. Trim beans to fit feed tube horizontally. With lid in place, stack beans in feed tube, then push beans through feed tube with food pusher while motor is running. OR, cut beans diagonally into 2-inch lengths with a sharp knife.
Add miso, sugar,mirin, lemon juice, soy sauce, and optional lemon zest to ground sesame seeds. Gently toss mixture with prepared beans. Garnish with a sprinkle of roasted sesame seeds before serving.