Finely chop the kimchi and onion.
Heat sesame oil in a pan and sauté the onion.
Add the kimchi and stir-fry over medium heat.
Add the tuna and stir-fry, mixing well.
Add the rice and stir-fry until all the ingredients are evenly mixed.
Taste and season with salt or pepper if needed.
Serve the finished fried rice in a bowl.