Slice your tuna into ½-inch slices.
Start making your sushi rolls by Spreading your rolling mat with a plastic wrap on top to easily clean up after.
Separate each nori sheet into two halves using a pair of scissors. Lay each half on the rolling mat.
On the nori sheet, put ¾ cup of the cooked rice. Wet your fingertips with tezu water before you start rolling the sheet. Make sure the rice form a thin sheet.
Spread the toasted sesame seeds evenly on top.
Transfer the slices of tuna on top of the rice.
With your thumbs beneath the rolling mat, lift the edge above the fillings and start rolling it away from you, all while gently yet firmly pressing on the roll.
Cut your roll into bite-sized pieces. Enjoy.