Heat the oil in a large pot over medium heat. Saute onion, garlic and 1/4 cup cilantrol until soft. Add chicken broth, chickpease, tomatoes, olives, marjoram, paprika, and salt and pepper to taste. Bring to a boil; lower heat and simmer 20 minutes. Add shredded chicken, simmer 5 minutes longer. Remove from heat; stir in zest and 1 tbsp cilantro.
Meanwhile, bring 2 cups water, butter and 1/2 tsp salt to a boil in a medium saucepan. Remove from heat, stir in couscous, and cover with tight-fitting lid. Let stand 10 minutes. Fluff with a fork before serving with stew.