Combine the water, sugar, vinegar and spices for the pickled vegetables in a small saucepan. Bring to a boil over high heat. Pour hot liquid, using a strainer to remove seeds, over shredded vegetables and let sit for half an hour or more. Refrigerate in a non-reactive airtight container if prepared in advance.
Using a mortar and pestle, grind the garlic, chili pepper, and sugar into a smooth paste. Add the lime juice and the Vietnamese fish sauce (if using the sambal sauce add it at this time) to the paste and stir. Add the water, to taste. Set aside.
To make the noodle "patties", bring a pot of water to a boil and add the noodles. Cook for 2 to 3 minutes, and then drain in a colander. Pat the noodles dry, place in a large bowl, and sprinkle with the rice flour. Toss to thoroughly combine. Lightly oil your hands, then, working 1 at a time, gather a small amount of noodles and shape into small nests about 2 to 3 inches wide. Repeat until you have at least 24 patties. (Any remaining noodles should be discarded.) Prepare a steamer and line with waxed paper. When the steamer water is boiling, steam the patties, patting them down to compress with a spatula, for 3 minutes. Transfer to a plate to cool slightly before serving.
To grill the shrimp, heat a grill pan or the grill to medium-high heat. Season the shrimp with salt and pepper. Lightly grease the pan or the grill with peanut oil and place the shrimp on the grill. Cook for 2 minutes on each side, or until the shrimp are just cooked through. Set the cooked shrimp aside, in a warm spot or lightly covered while assembling the rest of the dish.
In a small saucepan, heat 1 cup of peanut oil. Add the shallots in batches and fry to a golden brown, 2 to 3 minutes. Remove from oil and drain on paper towels. Season the shallots with salt as soon as they come out of the oil.
To eat the noodles, take a lettuce leaf, add the noodle "patty", spoon a little nuoc cham over noodles, add the pickled vegetables, herbs and sprouts, shrimp and shallots. Roll up to dip into the nuoc cham and then eat with your hands. Serve with hoisin sauce and sriracha sauce on the side for diners to season their rolls, if desired.