Combine the fish sauce, chiles, garlic, and the zest of the lime in a bowl. Squeeze all the juice of the lime into the mixture and add the sugar and coconut water. Whisk until sugar dissolves and set aside.
Bring a large pot of salted water to a boil and add the shrimp. Turn off the heat and let stand 2-3 minutes or until the shrimp are just cooked through. Remove with a slotted spoon to a bowl filled with ice water and let chill. Drain the shrimp well.
Meanwhile, bring the pot of water to a boil again and add the rice noodles. Turn off the heat and let stand 3-6 minutes or until softened. Drain in a colander and rinse with cold water. Drain well and toss with a few tablespoons of the fish sauce dressing.
To serve, line 4 plates or shallow bowls with the lettuce. Divide the noodles between the plates and top with the mango and shrimp. Sprinkle with peanuts, mint, and cilantro leaves and serve with the fish sauce dressing.