Heat the oil in a large skillet over medium heat. Sauté the onion until softened, about 3 minutes. Then add garlic and continue to sauté until fragrant, about 1 more minute. Set aside to cool.
Preheat oven to 400F.
Open and drain the cans of tuna and then transfer the tuna to a large mixing bowl. Next, add the mayonnaise, breadcrumbs, parmesan, parsley, oregano, reserved sautéed onions, lemon juice, and eggs. Mix until well combined.
Form the mixture into approximately 15 meatballs and place them on a lined baking sheet.
Bake at 400F for 20 - 25 minutes, or until golden.
Enjoy immediately over a swirl of tzatziki, serve with fresh lemon slices and an optional slice of toasted naan.
