In a bowl, whisk yogurt, harissa, lemon juice, 1 tsp. salt, and several grinds of pepper. Add chicken; turn to coat. "It's a little dry to start, but there's plenty of fat that comes out of the chicken," Fletcher notes. Chill, covered, 4 to 8 hours. "The acid in the yogurt helps tenderize the meat." Remove from refrigerator 30 minutes before cooking.
Preheat oven to 425° with a rack set in upper third. In a bowl, combine chickpeas, onion, and carrots. Season lightly with salt and toss to blend. Make a bed of the vegetables in a 9- by 13-in. baking dish. With a rubber spatula, redistribute marinade so it evenly covers both sides of chicken. Set chicken on vegetables, skin side up. Bake until chicken is deeply browned, about 45 minutes. "It should even be charred in spots."
Transfer chicken to a plate. Stir vegetables and add a splash of water if they look dry. Bake until carrots are tender, 10 minutes longer. Stir in 1/3 cup cilantro.
To serve, set chicken on vegetables and sprinkle with a little more cilantro.
*Find harissa, a Tunisian chile-and-spice paste, at well-stocked grocery stores.