Peel the prawns leaving the tails intact. Gently pull out the dark vein from each prawn back starting at the head end.
Cut the crust off the bread and cut the bread into twenty-five 3 cm (1 1/4 inch) cubes. With a sharp knife, make an incision in the top ot the bread three-quarters of the way through. Gently ease a prawn into the cut in each bread cube, leaving the tail sticking out. Cut 25 strips from the Nori measuring 1 cm (1/2 inch) X 15 cm (6 inch). Wrap a strip around the outside of each bread cube and secure with a toothpick.
Fill a wok or a deep heavy-based saucepan one third full of oil and heat until a cube of bread browns in 15 seconds. Cook the prepared cubes in batches for 1-2 minutes, or until the bread is golden and the prawns cooked through. Drain on crumpled paper towels, remove the toothpicks and season with salt. Serve topped with a teaspoon of the mayonnaise.