In a large mixing bowl, combine ground chicken, minced garlic, grated onion, chopped parsley, chopped mint, dried oregano, crumbled feta cheese, breadcrumbs, salt, and pepper. Mix gently until just combined.

Divide the mixture into four portions and shape each into a patty about ¾ inch thick, making an indentation in the center of each patty.

Heat a skillet over medium heat and add olive oil. Cook each patty for 5-6 minutes on one side until golden brown, then flip and cook for another 5-6 minutes until fully cooked.

While patties cook, prepare tzatziki by mixing Greek yogurt, grated cucumber, lemon juice, dill, and a pinch of salt and pepper until smooth.

Lightly toast burger buns in the skillet for 1-2 minutes until warm.

Assemble by spreading tzatziki on the bottom bun, adding lettuce, a chicken patty, and a slice of tomato, then topping with the other bun.