Step 1

Place rice in a sieve and rinse under cold running water until the water runs clear. Set aside to drain well.

Step 2

Place the rice and cold water in a medium saucepan. Place over high heat and bring to the boil. Reduce heat to low and cook, covered, for 15 minutes or until tender. Remove from heat. Lift the lid and cover with a clean tea towel. Replace the lid and set aside for 10 minutes.

Step 3

Transfer rice to a large glass or ceramic bowl. Drizzle with rice wine vinegar and sprinkle with sugar and salt. Use a flat spatula to gently fold the sushi seasoning through the rice. Fan the rice while folding to speed the cooling time. Cover dish with a damp tea towel.

Step 4

Combine the tuna, green onion, cucumber and mayonnaise in a small bowl.

Step 5

Fill a small bowl with cold water. Dip your hands and a 1/4 cup measuring cup in water and shake off excess water. Use the cup to scoop a portion of rice. Place the rice in the palm of one hand and use your fingers to shape into a bowl shape, about 1cm thick. Place 2 teaspoon of tuna mixture in the centre, then lightly press the rice mixture around the filling and use your hands to form it into a ball. Place a nori strip around the centre, wetting the end so it sticks. Place on a tray and sprinkle lightly with white and black sesame seeds. Repeat with remaining rice, tuna filling, nori and sesame seeds.

Step 6

Serve rice balls with soy sauce, wasabi paste and pickled ginger. Sprinkle with extra green onions to serve.