In the bottom of a tagine (or, in a heavy dutch oven), heat the olive oil until hot. Season the chicken thighs on both sides with the salt and pepper, and ground ginger and sear until golden brown on the skin side, 4 to 6 minutes. Turn the chicken thighs to the other side, add the onion and garlic, and continue to cook until the vegetables are wilted, about 4 minutes longer. Add enough broth or water to come halfway up the sides of the chicken pieces. Add the cinnamon sticks, bay leaf, ginger, and saffron and stir so that the spices are combined with the cooking liquid. Bring to a boil, cover, and reduce heat so that the sauce simmers, and cook the chicken, turning frequently, until tender, about 1 hour. Add the olives, and lemon peel and continue cooking, uncovered, until very tender and falling from the bone, about 30 minutes longer. Using a slotted spoon, transfer the chicken pieces to a serving platter and cover to keep warm. Increase the heat under the tagine and cook until the sauce is reduced to a thick consistency, about 10 minutes longer. Add lemon juice to taste if desired and discard the cinnamon sticks. Spoon the sauce over the chicken and serve immediately.