Make the mint yogurt: In a bowl, mixing the yogurt, mint, cumin and lemon zest. Set aside.
Place the lamb, spices and garlic into a large bowl and season well with salt and freshly ground black pepper. Shape into 4 burgers. Brush with a little oil and fry or barbecue for about 5 minutes on each side until cooked all the way through. Serve in toasted buns with the mint yogurt, tomatoes, red onion slices and a few mint leaves.