In a large mixing bowl, combine ground chicken, finely chopped onion, minced garlic, crumbled feta, and chopped parsley or dill. Add dried oregano, salt, black pepper, and red pepper flakes. Incorporate lemon zest, lemon juice, breadcrumbs or almond flour, and beaten egg. Mix gently without overmixing.

Divide the mixture into equal portions and shape into patties about ¾ inch thick, making a slight indentation in the center.

Cook the burgers on a preheated grill at medium-high heat for 6–7 minutes per side until they reach an internal temperature of 165°F, or pan-sear in olive oil for 5–6 minutes per side.

For baking, preheat the oven to 375°F, place the burgers on a lined baking sheet, and bake for 20–25 minutes.

For air frying, preheat the air fryer to 375°F and cook for 12–14 minutes, flipping halfway through.

Prepare tzatziki sauce by mixing Greek yogurt, grated cucumber, minced garlic, lemon juice, and chopped dill or mint in a small bowl. Season with salt and pepper to taste.

Assemble by placing each burger on a bun or pita, topping with tzatziki sauce, and adding fresh vegetables. Serve immediately.