Cook the rice vermicelli noodles according to package instructions. Drain and rinse under cold water to cool. Set aside.
In a large bowl, combine the shredded carrots, shredded red cabbage, cucumber, cooked shrimp, mint, cilantro, and green onions.
In a small bowl, whisk together the lime juice, fish sauce, sugar, sesame oil, minced garlic, and crushed red pepper flakes (if using) until the sugar is dissolved.
Add the cooled rice vermicelli noodles to the large bowl with the vegetables and shrimp. Pour the dressing over the salad and toss gently to combine.
Top with chopped roasted peanuts before serving.