Rinse the sushi rice under cold water until the water runs clear. Cook the rice according to package instructions.

In a small bowl, mix rice vinegar, sugar, and salt. Gently fold this mixture into the cooked rice while it's still warm. Let it cool to room temperature.

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

Place a bamboo sushi mat on a clean surface. Put a sheet of nori on top, shiny side down.

Wet your hands and spread a thin layer of rice evenly over the nori, leaving about 1 inch at the top edge free of rice.

Arrange your choice of fillings horizontally across the center of the rice.

Lift the edge of the mat closest to you and roll it over the fillings, tucking them in tightly. Continue rolling until the sushi is fully formed.

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