Rinse the sushi rice under cold water until the water runs clear. Cook the rice with water in a rice cooker or pot until fully cooked.

In a small saucepan, heat rice vinegar, sugar, and salt until dissolved. Gently fold this mixture into the cooked rice and let it cool to room temperature.

Prepare all fillings: slice the fish into thin strips, julienne the cucumber, and slice the avocado.

Take a half sheet of nori and hold it in your hand. Spread a thin layer of sushi rice on one half of the nori.

Add your choice of fillings (fish, cucumber, avocado) diagonally across the rice.

Roll the nori into a cone shape, starting from the bottom corner. Seal the edge with a little water or rice.

Serve immediately with soy sauce, wasabi, and pickled ginger on the side.