In a bowl, mix the onion strips with the sumac, ground cumin, salt, and pepper.
Rub the chicken (or chicken legs) all over with the onion-spice mixture, then drizzle lightly with olive oil.
Place the chicken and remaining onion mixture in a baking dish. Bake uncovered at 200°C (392°F) for 45 minutes until the chicken reaches an internal temperature of 74°C (165°F).