Prepare and Cook the Rice: First, place the sushi rice in a sieve and rinse it under cold running water until the water runs clear. This step is crucial for fluffy rice. Add the rinsed rice and 400ml of cold water to a medium saucepan. Bring to a boil, then reduce the heat to your lowest setting, cover with a tight-fitting lid, and let it simmer for 15 minutes. Do not lift the lid during this time.

Make the Rice Seasoning: While the rice is simmering, gently heat the rice vinegar, caster sugar, and salt in a small pan over a low heat. Stir until the sugar and salt have completely dissolved. Set it aside to cool slightly.

Rest the Rice: After 15 minutes, remove the rice from the heat and let it stand, still covered, for another 10 minutes. This allows the steam to finish cooking the grains perfectly.

Season the Rice: Transfer the cooked rice to a large, non-metallic bowl. Pour the vinegar mixture over the hot rice. Using a spatula or wooden spoon, gently fold the seasoning through the rice with a cutting motion. What works best for me is to avoid stirring, as this can mash the grains. Allow the rice to cool to room temperature. You can learn more about perfecting this technique from authoritative guides on sushi rice.

Mix the Spicy Tuna: In a separate mixing bowl, add the well-drained tuna, mayonnaise, Sriracha, soy sauce, and sesame oil. Mix everything together until the tuna is evenly coated in the creamy, spicy sauce. Taste and add more Sriracha if you prefer it spicier.

Assemble Your Bowls: Divide the seasoned rice among four bowls. Top each bowl with a generous scoop of the spicy tuna mixture. Artfully arrange the sliced avocado, cucumber, and sliced spring onions around the tuna.

Garnish and Serve: Finish by sprinkling over the toasted sesame seeds and the optional nori strips. Serve immediately and enjoy!