Cook the Noodles:
Boil rice noodles according to package instructions. Drain, rinse with cold water, and set aside.
Prepare the Dressing:
In a bowl, whisk together fish sauce, lime juice, rice vinegar, sugar, water, garlic, and red pepper flakes until sugar dissolves.
Assemble the Salad:
In a large bowl or plate, layer lettuce, noodles, carrots, cucumber, and bean sprouts. Top with herbs and protein of choice.
Dress and Toss:
Pour the dressing over the salad just before serving. Toss gently to combine.
Garnish and Serve:
Sprinkle with chopped peanuts and extra herbs for a burst of freshness.