Individual sushi rolls are cut from one long roll to reveal the filling hidden in the centre. For shaping the long roll you need to use a mat. Special bamboo rolling mats can be found in Oriental shops, or you can use an undyed, flexible straw place mat.
Lay tuna over the line of wasabi paste to cover it completely. You may need more than one strip of tuna.
Lift up the short end of the mat nearest to you and roll the nori around the rice, rolling it away from you.
Cut the long sushi roll across into four equal lengths, then cut each length in half to make eight pieces.