First, wash and clean the tuna steaks to remove any impurities.

Set the cooking time for 25 minutes. Meanwhile, thoroughly wash two 1-pint (about 1/2 kilo) jars and sterilize them by boiling them with their lids for 5 to 10 minutes (boil the lids just a few minutes so the seals aren't damaged). Drain and set aside.

Once the tuna is cooked and the pressure has released, remove the tuna from the pot and let it cool. Carefully remove all bones, skin, and, if you prefer, the dark parts of the tuna (which can have a strong flavor from the blood). Pour a little oil into each jar and swirl to coat the sides.

Place a piece of onion, a bay leaf, and a strip of bell pepper in each jar. Fill the jars with chunks of tuna, then pour in oil until it reaches the neck of the jar (where the threads start). Let the oil settle, then top off if needed. Seal the jars tightly.

Place a towel at the bottom of a large pot, set the jars on top, and fill with water. Bring to a boil and process for 20 to 25 minutes. This finishes the preservation process and creates a vacuum seal, ensuring no air remains and the product stays safe. Turn off the heat and let the jars cool completely.

Your homemade tuna preserves are ready! Store them in a cool, dry place. If everything is well sealed and sterilized, they will last a long time. If you plan to eat the tuna within a day or two, you can skip the canning process: after removing the skin and bones, cover the tuna with oil and your favorite spices, and keep it in the refrigerator.

Tip: To check if your jars are properly sealed and vacuumed, the button on the lid should stay down at all times.