In a small pan, fry in olive oil the minced garlic for a couple of minutes, then add the tomato sauce and season with salt and pepper.
Cook at low heat for 15-20 minutes.
For the Fritters
Grate the zucchini and chop the onion very thinly. Brown both in a pan with olive oil for about 10 minutes, until they become tender. Set aside and let them cool.
Drain the tuna and mix it with the egg, Parmesan, breadcrumbs, salt and pepper. (If the mix is too loose, add more breadcrumbs). Drain as much as possible the zucchini and onion, and add them to the mixture.
Add enough olive oil to coat well a large pan and wait until it gets hot (but not smoking).
Shape the mixture with your hands into a burger shape or spoon it directlly in the hot oil.
Turn them to brown both sides. As soon as they are uniformly golden brown, they're ready!
Serve them with freshly made garlic tomato sauce.
You can add a couple of tablespoons of Ricotta if you have it available. It will make the meatballs even more tender.