Heat the oven to 375°F (190°C).
Slice the sweet potatoes into 1/2-inch (1.3 cm) rounds and roughly chop the carrots into similar-size pieces. Arrange them in a large braiser or roasting pan.
Place the chicken pieces on top, drizzle lightly with olive oil, and sprinkle with a pinch of salt.
In a medium bowl, whisk together the olive oil, pomegranate molasses, honey, orange zest, cinnamon, salt, paprika, sumac, and cumin until thick and well blended. Slowly whisk in the orange juice until fully incorporated.
Pour the marinade evenly over the chicken and vegetables. Sprinkle the thyme leaves over the top. Cover the pan tightly with a lid or foil and roast for 1 hour.
Remove from the oven, uncover, and baste the chicken with the pan juices. Raise the oven temperature to 425°F (220°C) and roast uncovered for 30 to 40 minutes, until the chicken is browned and cooked through.
Arrange the sweet potatoes and carrots on a serving platter. Place the chicken pieces on top and spoon over all remaining pan juices. Garnish with pomegranate arils and extra thyme leaves before serving.