Combine the oil, garlic, rosemary, thyme, oregano, and peppercorns in a small bowl. Place the lamb in a resealable plastic bag. Pour the marinade over the lamb and seal the bag. Place in a bowl and refrigerate overnight.
Prepare a grill for direct cooking over high heat, or heat a grill pan until scorchingly hot. Remove the lamb from the marinade and discard marinade. Wipe any excess marinade off the lamb with paper towels. Sprinkle with salt. Grill the meat until medium rare, turning once, about 3 minutes on each side. Transfer to a platter, tent with foil and let rest 10 minutes before serving.