Cook vermicelli noodles according to package directions. Let cool.
DRESSING: Blend coconut milk with peanut butter, sesame oil, sriracha sauce, lime juice and fish sauce. Season with salt to taste.
In a large bowl, toss vermicelli noodles with prawns, carrot, cucumber, bell pepper, onion, tomatoes and peanut dressing. Serve garnished with chopped peanuts and cilantro (optional).