Bring broth to a boil in a medium saucepan, and gradually stir in couscous. Remove from heat; cover and let stand 5 minutes. Place couscous in a large bowl, and cool completely. Fluff with a fork. Stir in tomato, cucumber, and next 4 ingredients (through chickpeas); toss well. Combine oil and the remaining ingredients in a small bowl; stir with a whisk. Add vinegar mixture to couscous mixture just before serving; toss gently.