Preheat the grill to 350 F.
Rub the lamb with salt, pepper, and rosemary.
Grill on both sides until slightly browned, approximately 10 minutes per side or until a thermometer inserted into the thickest part of the meat registers 130 degrees.
Remove the lamb from the grill and cover loosely with foil. Let the meat rest for 10 minutes.
Slice the lamb in between the bones and serve right away.