1Put all of the dressing ingredients, including the chopped stems of cilantro but not the leaves, into the bowl of a blender or food processor and pulse until smooth.
2Meanwhile, cook or soak the rice noodles according to the package directions; drain well and rinse with cold water. Transfer to a large bowl and toss with the sesame oil.
3Add the reserved cilantro leaves, carrots, cucumber, red pepper, bean sprouts and onions; drizzle generously with dressing and toss with tongs to combine. Sprinkle with sesame seeds or chopped salted peanuts and serve.