In a large pot, boil water with a tablespoon of salt. Add edamame and boil for 3 minutes. Remove the beans from the pods, and set aside. Boil the pasta in salted water according to package instructions. Reserve 2 cups pasta water then strain in a colander.
In a blender (or food processor), pulse the edamame, garlic, ginger, miso, truffle oil, 1/4 teaspoon salt and red pepper flakes. Puree on high to form an extremely smooth paste, about 1 minute. You may need to scrape along the sides a bit to get the smoothest consistency. Feel free to add a splash of the pasta water.
To a large pot, mix the pasta water with the edamame paste over medium high heat to form a creamy sauce, about 2 minutes, whisking to break up clumps. Add the pasta and toss to combine. Serve hot with the green onion as a garnish.