Prepare all the ingredients.

Heat the cooked rice and place it in a bowl.

Add sesame oil to the rice and mix well.

Add sesame seeds to the rice mixture.

Mix in the canned tuna.

Add the canned corn to the mixture.

Add the chopped onion to the mixture.

Add mustard to the mixture and mix thoroughly.

Add a small amount of sugar to balance the flavors.

Shape the seasoned rice mixture into balls.

Roll the rice balls in crushed seaweed flakes.