Cook the sushi rice

• Rinse the sushi rice until the water runs clear, then drain.
• Cook the rice with the water in a covered saucepan until tender and the water is absorbed.
• Spread the rice on a tray to cool slightly.

Season the rice

• Warm the rice vinegar with the sugar and salt until dissolved.
• Sprinkle the vinegar mixture over the rice and fold gently to combine.

Make the spicy tuna

• Mix the chopped tuna with the mayonnaise, sriracha, sesame oil and soy sauce.
• Fold in the sliced spring onion.

Shape the rice buns

• Lightly grease small round moulds or ramekins with vegetable oil.
• Press the seasoned rice firmly into the moulds to form two buns per burger.
• Chill the rice buns so they hold their shape.

Toast the rice buns

• Sear the rice buns in a hot frying pan until golden and crisp on both sides.
• Sprinkle the toasted sesame seeds over the buns.

Assemble the sushi burger

• Place a rice bun on a nori sheet, then top with avocado and cucumber slices.
• Spoon the spicy tuna over the vegetables.
• Close with the second rice bun, wrap with the nori and serve.