Drain the cans of tuna into a fine sieve with a bowl underneath, gently flake the tuna to remove any excess oil, then transfer into a large bowl, along with the breadcrumbs, eggs, chopped shallot, grated garlic, chopped parsley, and season with sea salt & black pepper, mix together, then mash down on the mixture until you get a paste-like texture

Transfer the mixture over a clean flat surface, cut into 3 evenly sized pieces, then shape each one into a ball, making sure to squeeze the mixture in your hand, this is to ensure everything is well bound, then gently mash down on each ball to shape the patties, about 1 1/2 cm (5/8 inch) thick

Heat a large fry pan with a medium heat and add in the reserved olive oil from the canned tuna

After a couple of minutes add in the tuna patties, fry for 5 minutes per side or until cooked through and golden fried

In the meantime make the tzatziki, add the Greek yogurt into a bowl, then add the grated cucumber over some paper towels and squeeze the water out, transfer the cucumber into the bowl with yogurt, then add in the grated garlic, dried dill, lemon juice, and olive oil, then season with sea salt and a generous portion of black pepper, and whisk together until well mixed

Once the tuna patties are cooked through and golden fried, about 5 minutes per side, remove from the pan

To assemble the burgers, add some of the tzatziki over the bottom bun, then add one of the tuna patties, some sliced tomato, sliced red onion, and shredded lettuce, then add another dollop of the tzatziki over the top bun and place over the burger, enjoy!