Soak the seaweed in cold water for 10 minutes, then chop it into small pieces.
Prepare the oatmeal.
Boil water in a pot and blanch the seaweed for 2 minutes.
Add tuna (drained of oil) and stir well.
Add the oatmeal and simmer over medium heat for 5 minutes, stirring constantly.
Season with salt to taste.
Transfer the finished porridge to a bowl and serve.