Boil water and cook rice vermicelli 2–3 minutes until tender; drain and rinse under cold water to stop cooking.
Bring a pot of water to a simmer and briefly poach shrimp 1–2 minutes until opaque; transfer to ice water, drain, and slice lengthwise.
Prepare a clean work surface and arrange ingredients within reach: lettuce, herbs, noodles, veggies and shrimp.
Fill a shallow wide bowl with warm water. Dip one rice paper wrapper for 3–5 seconds until pliable; don’t over-soak.
Lay softened wrapper on the work surface. Place one lettuce leaf centered toward the bottom third of the wrapper.
Add a small handful of noodles on top of the lettuce, keeping a compact mound near the center.
Layer carrots, cucumber, a few cilantro and mint leaves, and a couple of scallion strips on the noodles.
Arrange two shrimp halves, cut-side down, near the top edge of the filling so they show through the wrapper.
Fold the bottom edge over the filling, then fold in both sides snugly and roll tightly away from you to close; ensure shrimp remain visible.
Repeat with remaining wrappers and fillings, keeping finished rolls covered with a damp towel to prevent drying.
Mix dipping sauce: stir fish sauce, lime, sugar and warm water until sugar dissolves; add garlic and chili to taste. Garnish with crushed peanuts and serve immediately.