Tekkamaki

Tuna sushi rolls are called tekkamaki in Japanese. 
Japanese Sushi Recipes
Ingredients:

4 cups sushi rice
4 sheets of nori (dried seaweed), cut in half
4 oz sashimi/sushi-grade tuna
Preparation:

Cut tuna into thin and long sticks. Put a nori sheet on top of a bamboo mat (makisu). Spread the sushi rice on top of the nori sheet. Place tuna horizontally on the rice. Roll up the bamboo mat, pressing forward to shape the sushi into a cylinder. Press the bamboo mat firmly and remove it from the sushi. Cut the rolled sushi into bite-sized pieces. 
*Makes 8 rolls