Preheat oven to 300 degrees, with rack in center. Set aside lamb, peanut oil and chicken broth. Add all remaining ingredients to food processor bowl and work into a coarse paste. The mixture will be thick and have some rough texture.
Untie lamb and sprinkle all sides with salt and pepper. Lay flat, inner side up and spread about 2/3 of the paste inside. Roll roast back together and tie firmly with twine, into an even log.
Over high heat, add peanut oil to a large, oven-proof skillet. When it begins to smoke, add lamb and sear undisturbed for 3 min; repeat until all sides are browned. Turn off heat, spread remaining paste over lamb, then roast in the oven 75-90 min, or until the center of the leg reaches 130 degrees for medium doneness.
Place lamb onto cutting board. Tent with foil and rest 15 min. Return skillet to stove, add chicken broth and cook on medium-high until sauce reduces and thickens. Taste sauce and adjust seasonings, if needed. Remove twine, slice lamb across the grain approx. 1/4″ thick.