Set the oven to 400°F. A fully heated oven helps the thin bread develop a crisp exterior.
Cut the red onions into slices, using a knife or a food processor fitted with a slicing attachment. The slices need not be paper-thin.
Combine the olive oil, sliced onions, and 1 teaspoon salt in a large sauté pan. Turn the onions through the oil so their surfaces become coated.
Maintain medium-low heat for 20 to 30 minutes, stirring every few minutes. Look for slumped, translucent onions with lightly golden edges rather than dark browning.
While the onions cook, stir the almonds in a separate skillet over low heat with 1 tablespoon olive oil, then set them aside once lightly toasted. The almonds should take on a pale golden color without dark spots.
Fold the shredded chicken, sumac, ground allspice, ground cinnamon, and remaining teaspoon salt into the softened onions. The warm mixture will release a fragrant, tangy spice aroma.
Keep the filling moving over the heat for another 5 to 7 minutes, then take the pan off the burner and fold in the almonds. The chicken should look evenly coated with onions and seasoning.
Divide the markouk into long strips, add about 1 to 2 tablespoons filling to each, and roll gently, folding in the ends if desired. The bread should enclose the filling without stretching or tearing.
Transfer the assembled rolls to an oiled 9×13 inch casserole dish. Keep the filling enclosed as you move each roll.
Bake for 25 minutes at 400°F, then broil for 5 minutes while watching closely. The bread should finish golden and crisp, without scorched edges.