Soak the seaweed in cold water, then drain the water.
Soak the oatmeal in the measured water for 5 minutes.
Heat sesame oil in a pot and sauté the soaked seaweed.
Add tuna and stir-fry together for 1 minute.
Add the oatmeal and water, and bring to a boil while stirring.
Simmer over medium-low heat for 5–7 minutes until the porridge thickens.
Taste and season with salt if needed.