Wash the mushrooms thoroughly and slice them into bite-sized pieces.
Drain the oil from the canned tuna and prepare it.
Heat olive oil in a pan and sauté the mushrooms.
Add the tuna and stir-fry together.
Add oatmeal and water or milk, then bring to a boil.
Season with salt and pepper.
Stir and cook until the porridge thickens.
Transfer to a bowl and serve.