Bring a pot of water to a boil and add the thin rice noodles. Cook according to package instructions, usually around 4-6 minutes, until just tender. Drain and rinse with cold water. Set aside to cool.

In a mixing bowl, combine the peanut butter, hoisin sauce, lime juice, and soy sauce. Whisk until smooth. Gradually add water to reach desired consistency.

Thinly slice cucumber, purple cabbage, red bell pepper, and grate or slice the carrot. Place chopped vegetables into a large mixing bowl.

Add the cooled rice noodles, chopped cilantro, and chopped mint to the vegetables. Toss in chopped peanuts if using. Mix gently until well combined.

Drizzle the peanut sauce over the salad mixture. Toss to coat each piece with the dressing.

Serve immediately or let it chill in the refrigerator for 15-30 minutes before serving.