Brown the chicken in butter and oil in a large, heavy skillet over moderate heat. Add the garlic cloves, spices, and coriander (chopped fine). Cook for about 10 minutes, turning the chicken pieces occasionally to distribute sauce evenly. Stir in enough water to cover, about 1 cup, and simmer over low heat, adding more water if necessary until the chicken is tender. Add olives and lemon and cook over somewhat higher heat for 8-10 moe minutes, or until sauce is reduced. Serve over rive couscous.