Combine harissa, garlic and olive oil in a shallow baking dish. Add lamb chops and turn to coat. Marinate at room temperature for up to 1 hour (or refrigerated up to 48 hours, just bring them to room temperature before grilling).
Preheat grill to medium heat. Sprinkle both sides of the lamb chops generously with salt and pepper. Grill for about 10 minutes for medium-well done, flipping once, or until desired doneness (about 8 minutes for medium-rare).