In a high-sided frying pan or braiser, combine the wine, cilantro, and peppercorns. Bring to a boil, reduce the heat, and simmer. Add the chicken and poach, turning once, about 12 to 15 minutes. Season to taste with salt and pepper. Remove to a cutting board to rest.
Meanwhile, bring the stock to a boil. Add the couscous, stir, and bring to a second boil. Remove from the heat, cover, and let stand 5 minutes. Stir in the turmeric.
Combine the charmoula ingredients in a small bowl. Cut the chicken breasts in half. Divide the couscous among 4 dinner plates and arrange chicken breasts on top. Serve each with 1/4 cup of the charmoula.