In a stockpot over high heat, bring about 8 cups of water to a boil. Add the noodles and cook until al dente, 7 to 10 minutes. Drain well and place in a large bowl. Set aside.
In a bowl, whisk together the remaining ingredients. Pour the dressing over the noodles and toss well. Let set at least 10 minutes before serving. Garnish with chopped scallions, if using.