Mix all the ingredients for dipping sauce together and stir until the sugar dissolves. It can be kept in the refrigerator for up to 1 week max
Use the knife to run through the back of the shrimp to remove the dark lines along the back. Keep the shells in tact, though (this is to prevent the shrimp from curling while being cooked). Bring a large pot of salted water to a boil. Drop in the shrimp (unpeeled), bring back to a boil, and cook just until pink and firm to the touch, 1 to 3 minutes. Lift out immediately with tongs or chopsticks and transfer to a plate to cool. Remove the shells when they are cool to touch. Set aside
Bring the water back to a boil. Cook the noodles for 2 minutes (or follow package instruction), or until soft, and drain. Refresh with cold water, drain, and set aside
Place a large bowl of warm water by your work area. Moisten a tea towel or cotton cloth thoroughly with water and lay it flat on the work surface. I didn't do this, but it is actually easier if you have a damp towel underneath as the rice paper won't be sticking to the plate. Working with 1 rice paper at a time, immerse the rice paper in the water. It will soften in less than 30 seconds. Lift it out and place it flat on the wet cloth
Lay 1 piece of fresh lettuce and herbs on the lower portion of the wrap. Place a small handful of noodles on top of the lettuce, spreading them in a line across the lettuce. Place 2 shrimp halves (orange sides down) next to the lettuce. Top with two thin slices of cha lua. Fold both sides up. Place 1 sliver of chive in the middle then fold the bottom portion of the wrapper up and continue to roll up and gently tuck in as you roll up so that the roll is tight and nice
Cover with a damp cloth or with plastic wrap, then repeat with the remaining rolls. Serve immediately, or set aside for up to 2 hours, covered with the damp cloth and plastic wrap to prevent the wrappers from drying out at room temperature. Serve on a platter or on individual plates, whole or cut crosswise in half
Use a small spoon to drizzle on the sauce as you eat mouthful by mouthful :)