Finely chop the kimchi and onion.
Heat cooking oil in a pan and stir-fry the onion and kimchi.
Add tuna and stir-fry, mixing well.
Add rice and stir-fry, mixing all the ingredients evenly.
Season with soy sauce and pepper.
Turn off the heat, add cheese on top, and cover with a lid to melt the cheese.
Transfer to a plate and serve.