Preheat the oven to 400°F. Line a baking sheet with parchment paper.
Pat the chicken legs dry and place on the prepared baking sheet.
Add 1 tablespoon of the seven spice, 1 teaspoon salt and 1 tablespoon sumac on top of the chicken.
Drizzle 2 tablespoons olive oil and use your hands to rub the spice mixture into the chicken, making sure to get underneath the skin.
Bake for 40 minutes until the skin is crisp and the chicken is cooked to internal temperature of 165°F.
Meanwhile, heat the ¼ cup olive oil in a large non-stick skillet over medium heat. Add the onions and cook, stirring occasionally until lightly golden.
Add the remaining seven spice, salt and sumac on top of the onions and continue cooking for 5 more minutes until the spices are fragrant.
Place the flatbreads on a large baking sheet.
Divide the onion mixture between the flatbreads. Spread the mixture but leave a small border around the edges.
Add one cooked chicken leg on each flatbread. Sprinkle the pine nuts on top.
Broil the flatbreads until the edges begin to brown and toast, 3-5 minutes.
Serve with lemon slices and fresh parsley, if desired.