Clean the fish by gutting and rinse the cavity, no need to scrub every part as that will not be used or even touched. There is no need to remove the head, fins, or skin, these will not be used.
Bring a pot of water to a boil, once boiling add the fish. Cook for about 20 minutes, the meat will start separate from the backbone and will flake easily with a fork.
When the fish is cooked through, remove the pot from the heat, cover, and let sit for about 20-30 minutes.
Once cooled, remove the fish from the water using a large wire scoop and place on a plate.
Using forks, pull back the skin and away from the meat. Then hold the tail and insert a fork near the tail area pointing towards the head and simply separate that side of meat from the backbone, flip over the tuna and do the same thing on the other side, discard the bones, head, and skin. Now you will have 2 nice big pieces of meat.
Now you have to remove the ribs, just use a fork and and lift the ribs out of the meat. There are no pin bones in this fish.
Now use the forks and chunk up the meat a little or a lot depending on what a recipe calls for. Place in a bowl and cover and refrigerate until used, This should last refrigerated for up 3 days. This makes several cans of tuna.
See, that was easy! You have fresh cooked "tuna", material for your compost pile, and no cans involved, all it takes is some time and effort on your part.