Finely chop the kimchi and onion.
Heat sesame oil in a pan and stir-fry the kimchi and onion.
Add tuna and stir-fry for a little longer.
Pour in water, oatmeal, and brown rice; bring to a boil.
Cook over low heat, stirring, until the porridge thickens.
Taste and season with salt or pepper.
Transfer to a bowl and sprinkle with sesame seeds.