Season the sushi rice with the rice vinegar, fanning and stirring until room temperature.
On the rolling mat place one sheet of nori with the rough side facing upwards.
In a small bowl, combine tuna filling ingredients. Set aside.
Wet your hands and grab a handful of rice and place it on the nori. Spread the rice evenly throughout the nori without smushing the rice down.
Arrange, in a horizontal row 1 inch (2 cm) from the bottom, a large spoonful of the tuna filling.
Grabbing both nori and the mat, roll the mat over the filling so the extra space at the bottom touches the other side, squeezing down to make a nice tight roll. Squeeze down along the way to keep the roll from holding its shape.
Transfer the roll onto a cutting board. Rub a knife on a damp paper towel before slicing the roll into six equal portions.