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

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.

Place a bamboo sushi mat on a clean surface. Cover it with plastic wrap to prevent sticking. Lay a nori sheet on top, shiny side down.

Wet your hands and spread a thin layer of sushi rice evenly over the nori, leaving a small border at the top. Sprinkle sesame seeds over the rice.

Carefully flip the nori and rice over so the rice is facing down. Place avocado, cucumber, and fish slices horizontally in the center of the nori.

Using the bamboo mat, roll the sushi tightly from the bottom, applying gentle pressure. Seal the edge with a little water if needed.

Slice the roll into bite-sized pieces with a sharp, wet knife. Serve with soy sauce, wasabi, and pickled ginger.