Place the rice noodles in a large bowl of hot water until softened, about 15 minutes. Drain and rinse with cold water. Fill a large bowl with hot water and soak the rice wrapper sheets one at a time until softened but still rather firm; about 20 seconds.
Place the sheets on a large tea towel, separate from each other. Place a mint leaf into the centre of each wrapper. Place two prawns halves over the mint leaf, top with a small handful of the noodles and 5 or 6 bean sprouts. Season to taste with fish sauce and garnish with coriander leaves.
Roll them, burrito style, by folding the bottom of the wrapper over the filling in the centre. Fold in the left and right sides, then roll the entire thing away from you tightly.