In a large bowl, mix the chicken with the sumac, onion, garlic, olive oil, allspice, oregano, lime, salt and pepper. Leave in the fridge to marinate for at least 5 hours or overnight.
Preheat oven to 400 degrees F. Transfer the chicken and its marinade to an 11x8-inch baking dish or larger dish (large enough to accommodate all the chicken pieces lying flat).
Roast in the oven until the chicken is colored and fully cooked through, about 40-50 minutes (cooking time depends on size of the pieces).
Serve the roasted sumac chicken with bread or rice.