Drain the tuna can and mash the tuna in a bowl using a spoon.

Chop 1/4 of an onion finely and add it to the mashed tuna.

Mix the tuna and onion with mayonnaise, sugar, salt, and sesame seeds until well combined.

Wash the cucumber thoroughly and use a peeler to slice it into thin sheets.

Prepare 1 cup of cooked rice and season lightly with sesame oil and salt for added flavor.

Place a cucumber sheet on a cutting board, shape the rice into small balls or logs, and place them on the cucumber.

Roll the cucumber around the rice tightly to form a roll.