Rinse the sushi rice under cold water until the water runs clear. Drain well.

Cook the rice with water in a rice cooker or pot. Once cooked, let it sit covered for 10 minutes.

Mix rice vinegar, sugar, and salt in a small bowl. Gently fold this mixture into the cooked rice while fanning to cool it.

Place a nori sheet on a bamboo mat. Spread a thin layer of rice evenly over the nori, leaving a small border at the top.

Arrange slices of fish, avocado, and cucumber in a line near the bottom edge of the nori.

Roll the sushi tightly using the bamboo mat, pressing gently. Wet the border to seal the roll.

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