Cut off the end of the cucumber and cut the cucumber in half lengthways, then slice it thinly on the diagonal.
Drain the tinned tuna.
Mix the sushi vinegar ingredients in a bowl.
Once the rice is cooked, put the rice in another bowl, then pour the vinegar mixture over the rice.
Gently mix the rice in a cutting motion with the rice paddle while fanning it with a paper fan or a piece of paper to cool.
Place the seaweed on a bamboo mat, place 1/5 of the rice leaving some space at the front and at the other side and spread it all the way to left & right sides with damp hands.
Lay some cucumbers or the tuna horizontally toward you from the center of the rice and sprinkle on some sesame.
While holding the ingredients in place, lift up the front of the bamboo mat and let it touch the other side of the mat. Gently push the roll into the shape by rolling the bamboo mat a little to tighten the roll.
Remove the bamboo mat and cut the roll into bite-sized pieces. ※ Wiping the knife with wet kitchen paper after each cut will keep the rice from sticking to the knife.