1.Rinse rice under cold water until water runs clear. Place rice and the water in medium heavy- based saucepan over high heat; bring to the boil. Reduce heat; simmer, covered, 12 minutes. Remove rice from heat; stand, covered, 10 minutes.
2.Tip rice into large wide bowl. Using a flat wooden spoon or spatula, cut and slice the combined vinegar, sugar, salt and mirin through the rice.
3.Line 19cm x 30cm lamington pan with plastic wrap extending 5cm over long sides of pan. Trim and position nori sheets to cover base of pan in single layer. Press rice over nori. Spread wasabi over rice. Top wasabi with single layer of salmon; press down gently. Cover pan; refrigerate until ready to serve.
4.To make the pickled green onion, combine ingredients in medium bowl; cover, refrigerate at least 1 hour to allow onions to curl.
5.Lift sushi from pan to chopping board; using large, heavy, wet knife, cut sushi into 4cm squares. Top sushi squares with drained pickled onion. Serve with japanese soy sauce for dipping.
Wet hands before pressing the rice over nori in pan, this will help prevent the rice sticking.Note