Preheat oven to 375 degrees F.
Place the lamb in a resealable plastic bag. Combine the marinade ingredients in a glass bowl or measuring cup. Pour the marinade over the lamb, seal the bag, and refrigerate for at least 1 hour or overnight.
Once marinated, place the lamb in a cast iron pan with olive oil and sear the lamb on all sides. Cover pan with tinfoil and place in oven. Roast the lamb until done, for about 2 to 2 1/2 hours. The internal temperature should reach 180 degrees F on an instant-read thermometer.