Preheat the oven to 450°. In a bowl, toss the chicken with 2 tablespoons of the oil and the coriander; season with salt and pepper. Arrange the chicken on a rack set over a baking sheet, skin side up. Roast in the upper third of the oven for 35 minutes, turning twice, until the chicken is cooked through. Turn on the broiler and broil for 2 minutes, until the skin is crisp and golden.
Meanwhile, in a bowl, toss the couscous with the pistachios, pomegranate seeds and 1/2 cup of the parsley. In a blender, puree the hummus and vinegar with the remaining 1 cup of parsley and 1/4 cup of oil. Add 2 tablespoons of water and puree until smooth. Season the dressing with salt and pepper.
Stir one-third of the dressing into the couscous and transfer to a platter. Arrange the chicken on top and serve right away, passing the extra dressing on the side.