Take one nori sheet. Cut in half lengthwise, then cut 3/4 inch from bottom of each sheet. You should have 2 sheets, each about 4 x 6 1/2 inches. (Scraps can be used for nori belts.) Repeat to cut remaining nori sheets.
Place a nori sheet lengthwise on a bamboo rolling mat, shiny-side down.
Position nori sheet about 1 inch from edge of mat closest to you, and leave some space on each side of nori sheet.
Wet your hands and take a golf ball – sized handful of sushi rice. Gently squeeze rice into an oblong ball and put on center left of nori sheet. Then use your fingers to squeeze rice into a log along center of nori.
Spread rice evenly over nori, working from left to right, leaving a 3/4-inch strip of nori on far side uncovered.
Build a low ridge of rice in front of this nori strip. This will keep the filling in place.
Take a dab of wasabi on your finger and wipe from left to right across center of rice (if you hold your finger at an angle to start and flatten it out at end, wasabi will spread evenly).
Place tuna strips along center of rice, over wasabi.
Place fingers flat over tuna strips to hold them in place, then use your thumbs to lift up edge of bamboo rolling mat closest to you.
Roll rolling mat away from you, pressing tuna in to keep roll firm. Lift rolling mat over slowly until it covers rice and near side and far sides of rice join at ridge, but you still have a 3/4-inch strip of nori rice-free.
Covering roll (but not rice-free strip of nori), hold rolling mat in position and press all around to make the roll firm. Use your index fingers on top and fingers and thumbs on side to press roll together gently.
Lift up top of rolling mat and turn roll over a little more so that strip of nori on far side joins other edge of nori to seal roll. Use your fingers to make sure roll is properly closed.
Roll entire roll once more, exerting gentle pressure.
Slice roll in half, then cut both rolls twice to give 6 equal-sized pieces. Repeat with remaining nori and rice.
Recipe reprinted by permission of Periplus. All rights reserved.