Combine half the lemon zest, cucumber and Greek yogurt in a small serving bowl; set aside. Heat half the oil in a large frying pan over medium heat. Add the chopped onion and garlic. Cook, stirring, for 3-4 minutes or until onion softens. Remove from heat and set aside.

Combine onion mixture, chicken mince, breadcrumbs and tarragon and remaining lemon zest in a large bowl. Divide mixture into 8 even portions and shape into patties.

Heat remaining oil in large non-stick frying pan. Add the patties and cook for 4 minutes each side or until brown and cooked through. Transfer to a plate, drizzle with lemon juice and cover with foil to keep warm.