In a large deep frying pan or Dutch oven, heat the oil over moderately high heat. Sprinkle the chicken with 1/2 teaspoon of the salt and the black pepper. Put the chicken in the pan and brown well, about 8 minutes in all. Remove. Pour off all but 1 tablespoon of the fat. Reduce the heat to moderately low.
Add the onion and turnip and cook, stirring occasionally, for 3 minutes. Stir in the tomato paste, paprika, cumin, cayenne, and 2 1/4 teaspoons of the salt. Cook, stirring, for 1 minute. Stir in 4 cups of the water and the carrots. Add the chicken and bring to a simmer. Cover and cook, stirring the mixture two or three times, until the chicken and vegetables are almost done, about 20 minutes. Stir in the chickpeas and the parsley and simmer until the chicken and vegetables are done, about 5 minutes longer.
Meanwhile, in a medium saucepan, bring the remaining 2 cups water to a boil. Add the remaining 1/4 teaspoon salt and the couscous. Cover. Remove the pot from the heat and let the couscous stand for 5 minutes. Fluff with a fork. Serve the stew with its broth over the couscous.
Wine Recommendation: Often with a complex dish it's best to serve a simple wine that won't compete with the food's flavors. Here, an exuberantly fruity Beaujolais-Villages will effectively highlight the stew.