Pre-heat the oven to 400°F with the rack in the middle
Make the spice rub in a good sized bowl that'll fit all the chicken pieces
Rub the chicken pieces down with olive oil, separating the skin from the meat but leave the skin intact
Rub the spice mix under the skin and on top of the pieces of chicken
In a roasting pan, combine the raw rice, pine nuts, barberries, turmeric, salt and 2 tablespoons of olive oil. Stir until the rice is a beautiful yellow color, and spread the rice out so it's pretty flat
Top the rice with the circles of red onion and lay the chicken pieces on top of the onions. Top each piece of chicken with a lemon slice
If you are assembling ahead of time and roasting later, this is the point you will want to cover the roasting pan with aluminum foil or lid and set in the fridge
Pour the stock gently around the chicken into the rice
Cover the roasting pan tightly with aluminum foil and place it in the oven. Roast for 40 minutes
Remove the foil and sprinkle an additional 1/4 cup sumac across the dish
Continue roasting for an additional 30-40 minutes until the chicken is cooked through and the rice has soaked up all of the liquids