1. Preheat oven to 500 to 550 degrees Fahrenheit (if it goes that high).
2. Place duck in a deep 9×13-inch pan and rub olive oil on the outside and inside of the duck. Season with fresh pepper and salt.
3. Rub three-fourths of the minced garlic, one tablespoon ginger, one tablespoon allspice, and half of the orange zest on the inside of the duck.
4. Rub remaining garlic, one tablespoon ginger, one tablespoon allspice, and half of the orange zest on the outside of the duck. Sprinkle with sumac.
5. Squeeze quartered oranges over the duck, then stuff a few squeezed orange segments, rosemary sprigs, and a cinnamon stick inside the duck.
6. Tie the legs and cap with cooking twine.
7. Place the duck, breast-side down, in the pan, and add any leftover orange segments, rosemary, and a cinnamon stick to the pan.
8. Cook, uncovered, on 500 degrees Fahrenheit for 40 minutes, or on 550 degrees Fahrenheit for 30 minutes.
9. While duck is cooking, halve the potatoes and toss with onions, garlic, olive oil, rosemary, salt, and pepper.
10. After 30 or 40 minutes of cooking, remove most of the duck fat and pour over the potatoes.
11. Decrease oven temperature to 425 degrees Fahrenheit.
12. Cover potatoes and cook for one hour and 10 minutes. Cover duck and cook for one hour and 15 minutes.
13. Uncover potatoes and broil on high for an additional nine to 11 minutes.
14. Let duck rest, uncovered, for 15 minutes before serving.