Using a sharp knife, cut lamb at the joint into two sections: a long, narrow piece and a wide, rounded piece. Place in a shallow bowl. In a small bowl, combine garlic, herbs, oil, and pepper. Using your hands, rub mixture over both lamb pieces to coat evenly. Cover with plastic wrap, and place in refrigerator; let marinate at least 1 hour and up to 6 hours. Remove from refrigerator about 30 minutes before cooking.
Meanwhile, heat grill; position rack about 6 inches above flame. Season lamb with salt; grill about 9 minutes on each side, or until a meat thermometer inserted into the center registers 135 degrees for medium rare. Transfer to a platter; loosely cover with foil. Let rest 15 minutes before slicing and serving.