We love this dish. Everything can be made ahead and yet it cooks rather quickly. The lamb needs to marinate overnight, and the relish can be made 1 month in advance. This sauce is so good, we use it on all kinds of meats and seafood. The recipe makes about 3 cups of sauce. Time does not include marinating time.
1Cut lamb into 2 pieces where there is a natural separation in meat and put each piece into a large sealable plastic bag.
2In a food processor, puree all remaining ingredients (except relish) until smooth and divide marinade evenly between plastic bags. Seal bags, pressing out excess air, and put in a shallow baking pan. Marinate lamb, chilled, turning bags once or twice, at least 8 hours or overnight.
4Discard marinade and grill lamb in batches if necessary on an oiled rack set 5 to 6 inches over glowing coals 7 to 10 minutes on each side for medium-rare. Transfer lamb to a cutting board and let stand 10 minutes.
5Serve lamb, thinly sliced across the grain, with relish.
6Hot Red Pepper Relish:
In a heavy saucepan, stir together ingredients and simmer, stirring occasionally, about 1 hour, or until reduced to about 3 cups. Relish may be made 1 month ahead and chilled, covered.