Place the chicken in a bowl and add the lemon juice; 3 tablespoons olive oil; 1 ½ tablespoons sumac; the garlic, cumin, allspice, and cinnamon; and 1 ½ teaspoons salt and ¼ teaspoon pepper. Rub the mixture into the meat.
Add the red onion and toss to coat. Cover and transfer to the refrigerator to marinate, for 1 to 3 hours.
Heat the oven to 375°F.
Transfer the chicken, onion slices, and any juices to a baking sheet and roast until the juices run clear for approx. 40 minutes.
In a small skillet, cook the pine nuts in the remaining 1 tablespoon olive oil until golden brown, then transfer to a paper towel to drain.
To serve, heat the bread and transfer it to a platter. Arrange the chicken and red onion on top.
Finish with a smattering of pine nuts, sumac, and chopped parsley.
Drizzle any remaining roasting juices so they soak into the bread, then drizzle with a little more olive oil and enjoy!!
