Put 4 cups of the water in a nonreactive medium-size saucepan over medium-high heat. Squeeze the lemon and add the juice and peel to the water. Add 1 teaspoon of the salt and the cayenne. Bring to a boil.
Season the shrimp with the shrimp and crab boil. Add the shrimp to the boiling water and cook for 2 minutes, stirring occasionally. Remove from the heat and let sit for 2 minutes. Drain and cool.
In another saucepan, combine 4 cups of the water and 1/2 teaspoon of the salt and bring to a boil. Add the noodles and boil until they are clear, about 2 1/2 minutes, stirring occasionally. Drain and cool with cold water. Put the noodles in a small mixing bowl and toss with the sesame oil, soy sauce, the remaining 1/4 teaspoon salt, the green onions, and black pepper.
Cut the shrimp in half lengthwise.
Bring the remaining 2 cups water to a boil in a 10-inch sautČ pan and remove from the heat.
Line a baking sheet with parchment or waxed paper.
Submerge each spring roll wrapper, one at a time, in the hot water, moving it around in the water until soft and pliable, 10 to 15 seconds. Remove and lay on the parchment paper.
Brush each wrapper with 1 teaspoon of the hoisin sauce. Lay a half leaf romaine in the center of each wrapper. On top of each half leaf, put 1 tablespoon of the noodle mixture and spread evenly. On top of the noodles, sprinkle 1 tablespoon of the sprouts. Top with 1 tablespoon of the carrots, 1 tablespoon of the cilantro, and 1 tablespoon of the mint. Lay 6 halves of shrimp next to each other on top of each mixture. Fold two sides of the wrapper toward the center about 1/4 inch, then roll each like a jelly roll, pressing the edges together to seal. Repeat until all eight rolls are done.
When ready to serve, cut each roll in half diagonally. Serve chilled or at room temperature with the dipping sauce.
Yield: 8 servings