Put the lamb steaks in a freezer bag, then add the garlic, oil, lemon zest&juice, and most of the mint. Tie the bag, then shake it and massage the steaks through the bag to cover them well with the marinade.
Rest in fridge for a couple of hours or even overnight.
Take the meat out of the bag, then season with salt an pepper.
Grill or barbecue over medium heat for a couple of minutes on each side - depending on the thickness of the steaks and how well cooked you like your lamb.
Serve with the remaining mint leaves scattered on top.