Soak the seaweed in cold water, then chop it finely.
Drain the oil from the canned tuna and set aside.
Prepare the cooked rice.
Pour water into a pot and bring to a boil.
Add the seaweed, tuna, and rice to the boiling water and stir.
Season with soy sauce and salt to taste.
Simmer over low heat until the porridge thickens.
Transfer the finished porridge to a bowl.