In a large bowl, combine ground chicken, minced garlic, grated onion, chopped parsley, mint, dried oregano, crumbled feta, breadcrumbs, salt, and black pepper. Mix gently until well combined and shape into four patties.

Cover the patties with plastic wrap and refrigerate for at least 30 minutes to enhance flavor and firmness.

Heat olive oil in a skillet over medium heat and add patties. Cook for 5-6 minutes per side until golden brown and internal temperature reaches 165°F.

In a small bowl, combine Greek yogurt, grated cucumber, lemon juice, chopped dill, salt, and pepper. Mix until creamy and set aside in the refrigerator.

Toast the burger buns in the same skillet for about 1-2 minutes until golden brown.

Spread tzatziki on the bottom half of each bun, add a lettuce leaf, a chicken patty, a tomato slice, and top with the other bun.