To prepare sauce, combine first 6 ingredients in a small bowl, stirring well with a whisk.
To prepare rolls, add cold water to a large, shallow dish to a depth of 1 inch. Place 1 rice paper sheet in dish of water; let stand 2 minutes or until soft.
Place softened rice paper sheet on a flat surface. Place 1 lettuce leaf on the bottom third of the sheet. Top with 1 tablespoon each of noodles, sprouts, cucumber, carrot, mint, and cilantro; add 2 Lemongrass Beef strips.
Fold sides of rice paper sheet over filling; roll up jelly-roll fashion. Gently press seam to seal; place, seam side down, on a serving platter (cover with a damp cloth to keep from drying). Repeat procedure with remaining rice paper sheets, noodles, vegetables, herbs, and beef. Serve with sauce.