Place a sushi mat flat on your work surface with the bamboo slats running from left to right, allowing you to roll the mat away from you. Position a sheet of seaweed on the sushi mat with one of its sides close to the front edge of the sushi mat (the edge near you). Spread about 1 cup of sushi rice on the seaweed, leaving a 1″ (2.5cm) space along the far edge of the seaweed. Put the tuna mixture in the middle of the rice. While holding the filling down, roll from the front end of the mat toward the other end. Tighten the roll, similar to a roll cake, by pulling the mat to tighten. Remove the roll from the mat.
