In a large pot, bring water to a boil. Remove from heat and add rice noodles. Let sit until tender, 5-10 minutes. Drain, rinse with cold water, drain again, and set aside. Place each ingredient in a separate bowl around your work station. Fill a wide (at least 9 inch) pan or bowl with hot water, 1/2-1 inch deep.
Working with 1 sheet at a time, place rice paper wrapper in hot water and press to submerge for 15 seconds. Remove from water, lifting up to remove excess water. Place on work surface.
On the bottom third of the sheet, place about 1/4 cup of the rice noodles, a few pieces of lettuce, mint, cilantro, and green onion slices.
Lift the edge of the wrapper closest to the ingredients and roll over once, tucking and closing in the filling. Tightly fold in the sides and place 2 shrimp halves, cut side down, side by side on the roll. Finish rolling up the wrapper, enclosing the shrimp. Set on serving plate, seam side down. Repeat with remaining wrappers.
Serve immediately with dipping sauce.