Bring a pot of water to a boil. Cook the rice noodles according to package directions, about 3 minutes, until tender. Drain and rinse under cold water, then set aside.

While the noodles cook, season the shrimp with a pinch of salt. Heat the oil in a skillet over medium-high heat. Add the shrimp and sear 2 to 3 minutes per side until pink and curled. Remove to a plate.

In a small bowl, whisk together the lime juice, fish sauce, sugar, garlic, and chili (if using) until the sugar dissolves.

In a large bowl, combine the drained noodles, carrot, cucumber, mint, cilantro, and shrimp. Pour most of the dressing over and toss well. Divide between plates, top with peanuts, and drizzle any remaining dressing on top. Serve right away.