Finely chop aged kimchi and onion.
Drain the oil from the canned tuna and prepare it.
Heat cooking oil in a pan and stir-fry the aged kimchi and onion.
Add the tuna and stir-fry together.
Season with soy sauce, sugar, and pepper.
Place the stir-fried aged kimchi and tuna mixture over rice.
Finish by sprinkling sesame seeds and chopped green onions.