Fill a large bowl with warm water. The bowl does not need to fit the entire rice paper in one go, as rotating works just as well.
If using two sheets of rice paper per roll, stack them together. Identify the smooth side of the paper—this should be the exterior of the roll. Submerge the rice paper into the warm water for about 2 seconds. If the bowl is smaller, rotate the paper and submerge each section for the same amount of time.
Lay the softened rice paper flat on a clean surface, ensuring the smooth side faces downward.
Near the top of the rice paper, arrange three prawn halves in a row, with a mint leaf placed between each.
Position the lettuce bundle in the center of the rice paper with the seam side facing down.
Fold in the left and right edges to enclose the filling, then begin rolling from the bottom. Tightly roll the paper over the lettuce bundle, continuing to roll firmly until sealed. The rice paper’s natural stickiness will secure the roll.
If arranged properly, the finished rolls should display the prawn and mint leaves through the translucent rice paper on the outer surface, with the seam neatly tucked underneath or along the side.