Soak the seaweed in cold water for about 10 minutes and cut it into small pieces.
Finely chop the onion.
Drain the oil from the canned tuna and set aside.
Add sesame oil to a pot and sauté the onion and seaweed.
Add the tuna and stir-fry together.
Pour in 400ml of water and bring to a boil.
Once boiling, add oatmeal and simmer on medium-low heat for 3-5 minutes, stirring from time to time.
Season with salt to taste.