Cut the chicken into cubes season with all the spices, add the chopped onion and the oil. Combine well and let it marinate for 20 minutes.
Heat the olive oil in a large skillet. Add the sugar, let it bubble up and get brown and then throw in the chicken, and sear it well on all sides until it gets golden dark brown on all sides. Add water along with the marinade juices enough to cover the chicken. Add the potatoes, lemon and olives. Let it simmer until chicken is tender, about 15 minutes. Add half of the cilantro and parsley, mix will let this simmer for 5 more minutes.
Arrange the meat and the potatoes on a serving platter, pour the sauce over the meat. Garnish the tajine with the rest of the parsley and cilantro.