In a large mixing bowl, combine cooked rice, sesame oil, mayonnaise, and canned tuna. Mix until cohesive.

If the mixture is too dry, add more mayonnaise until desired texture is achieved.

Flatten the mixture and cut into 8 triangular portions.

Roll each triangular portion into a tightly packed ball.

Serve immediately or refrigerate in an airtight container for up to 2 days.