Finely chop the aged kimchi and onion.
Beat the eggs and season with salt.
Stir-fry tuna in a pan, then add the chopped onion and cook together.
Place the chopped kimchi on top of the cooked tuna and onion and stir-fry together.
Pour the egg mixture widely into the pan, cook halfway, then add the stir-fried ingredients on top.
Carefully roll up the egg and cook until fully done.
Slice into bite-sized pieces and place on a plate.