1 (8-1/2 to 9 pound) Leg of lamb
1 Garlic clove, sliced
2/3 Cup all-purpose flour
1 Teaspoon salt
1 Teaspoon dry mustard
1/2 Teaspoon pepper
2 Tablespoon chili sauce
2 Tablespoons olive oil
1 Tablespoon Worcestershire sauce
1 Tablespoon vinegar
2 Medium onions, sliced
1 Cup boiling water
Trim excess fat from leg of lamb. Using a sharp knife, cut several small slits on outside of lamb; stuff with garlic slices. Combine flour, salt, ginger, mustard, and pepper, stirring well; rub over surface of lamb. Set lamb aside.
Combine chili sauce, oil, Worcestershire sauce, and vinegar, stirring until blended. Set sauce aside.
Place lamb, fat side up, in a shallow roasting pan. Insert meat thermometer into lamb. Arrange onion slices around lamb. Baste with sauce.
Bake uncovered, at 400 F for 25 minutes. Reduce heat to 350 F, and bake an additional hour and 15 minutes or until thermometer registers 140 F (rare) or 160 F (medium). Baste lamb every 15 minutes with sauce. Add boiling water to pan during last hour of baking time.
Transfer lamb and onion slices to serving platter, discarding pan drippings. Let stand 10 minutes before slicing. Serve lamb with remaining sauce.