Boil your eggs and cool them. Carefully peel the eggs, keeping the surface of the egg smooth and not dented. Cut in half with a sharp knife, then remove the yolks. Some of them will pop right out, but others will have to be scooped out. Be sure not to break the white while doing this. Gather the yolks and add a nearly equal volume of canned tuna. This time I also added capers (small, nonpareil ones), but that's optional. At this point you can mince with a mezzaluna or even work the mixture with a fork. Some use a food processor. Then add mayonnaise a bit at a time until you get the desired consistency. It should be fairly smooth and moist. Add salt (and pepper, if desired). Be careful if you've added the capers to take that into account.
That's it. Good with a fresh salad with carrots and fennel, crusty bread and white wine. If used as an appetizer, you may try putting little toppings on the eggs, such as a half green olive, a cocktail shrimp, a bit of crunchy cornichon, a thin slice of roasted red pepper, a tiny sprig of dill.