Crush the saffron threads and soak them in 3 tablespoons of warm water for 5 minutes.
Heat the olive oil in the tagine base (on a heat diffuser) or in a heavy pot over low to medium heat. Add the onions, garlic, ginger, turmeric, pepper, and cumin and paprika if using. Stir for 2 minutes.
Add the chicken and turn it in the spiced onions for about 10 minutes, until the skin takes on color.
Add the saffron water, the water and half of the herbs. Cover and simmer gently for 45 minutes, until the chicken is tender. Add a splash of water if the sauce gets too low.
Add the preserved lemon and olives. Simmer uncovered for 10 to 15 minutes, until the sauce thickens.
Taste and add salt only if needed. Top with the rest of the herbs and serve from the pot with bread.