In a blender blend sauce ingredients with salt and pepper to taste until smooth. Sauce may be made 3 days ahead and chilled, covered. Bring sauce to room temperature and stir before using.
Just before serving, in a 6-quart kettle bring 5 quarts salted water to a boil and cook spaghetti until al dente. In a colander drain spaghetti and rinse well under cold water. Drain spaghetti well and in a bowl toss with sauce and chopped coriander.
Garnish sesame noodles with cashews and coriander.