Rinse rice under cold water and drain. Bring water and rice to the boil, lower heat, cover and simmer for 12 minutes until water is absorbed and rice is tender, stirring occasionally.
Combine vinegar and sugar, stir until sugar dissolves and pour over rice stirring well. Spoon rice into a shallow dish and refrigerate for 5 minutes to cool quickly. Place a seaweed sheet on a bamboo mat. Spoon over a thin layer of cooked rice leaving a 1cm space at the top end.
Spread a little wasabi paste in a horizontal line along the middle of the rice. Mix mayonnaise with John West Tuna and spoon mixture along the wasabi line. Top with a strip of capsicum and shredded lettuce.
Holding the edges of the mat nearest to you, roll up tightly. Wrap in plastic wrap and refrigerate until required. Repeat with remaining seaweed sheets. Cut into thin slices and serve with salt reduced soy sauce.