To prepare chicken, combine the first 11 ingredients in a large zip-top plastic bag. Seal and marinate in refrigerator 24 hours, turning bag occasionally. Remove chicken from bag, discard marinade.
Place the chicken thighs on a broiler pan coated with cooking spray. Broil 4 inches from heat for 10 minutes or until a meat thermometer registers 180°.
To prepare the couscous, bring the broth to a boil in a medium saucepan, and gradually stir in couscous. Remove from heat; cover and let stand for 5 minutes. Fluff with a fork. Stir in the currants, onions, and 1/4 teaspoon black pepper.