1 boneless leg of lamb, rolled and tied
1 cup dry red wine, such as Pinot Noir or Cabernet Sauvignon
1/3 cup orange juice
1/4 cup chili sauce
1/4 cup water
1/2 cup minced onion
2 tablespoons vegetable oil
1 tablespoon chili powder
1 tablespoon brown sugar
1 teaspoon ground cumin
1/2 teaspoon dried leaf oregano, crumbled
1/2 teaspoon salt
1/2 teaspoon ground black pepper

Place the lamb in a deep nonreactive pan (stainless steel, enamel-lined, or glass). Combine remaining ingredients in a bowl; pour over the lamb. Turn to coat well. Cover and refrigerate overnight or for up to 24 hours, turning occasionally. Drain lamb; place on a rack in a roasting pan. Roast in a preheated 450 degrees oven for 15 minutes. Reduce temperature to 350 degrees . Pour marinade over the lamb and continue roasting, basting frequently, for about 2 to 2 1/2 hours, or until done to about 170 degrees to 175 degrees for medium. Add a little boiling water to prevent juices from cooking down and burning. Let roast stand for 10 minutes. Carve and serve with skimmed pan juices.
Serves 8.

Source: http://southernfood.about.com