Finely chop oatmeal, kimchi, tuna, and onion.
Heat sesame oil in a pot and stir-fry onion and kimchi.
Add tuna and stir-fry together.
Add oatmeal and water or broth, then bring to a boil.
Simmer while stirring until the porridge thickens.
Season with salt or other seasonings, and serve in a bowl.