Cut the preserved lemon in half and separate the flesh from the peel. Set the peel aside and finely chop the lemon pulp.
Place the chopped lemon pulp in a bowl, casserole or large heavy pot. Add the olive oil, smen, garlic, parsley, cilantro, spices, and a cup of cold water. Mix well.
Add the chicken pieces to the tagine and pierce them with a sharp knife so that they absorb the spices. Mix all the combined ingredients with the chicken pieces until they're well coated with the marinade.
Add the finely chopped onion to the tagine. Mix well.
On low heat, sear the chicken pieces for 15 minutes. The tagine lid should be on to keep the moisture in, otherwise the chicken pieces will dry out and stick to the bottom of the pot. Turn each piece of chicken over and add a bit of water if necessary.
After 15 mintues, add 1 cup of cold water. Increase the heat to medium, cover the tagine and bring the cooking juices to a boil. Cook, covered, for 30 minutes or until chicken is done. Check on the chicken from time to time and add water if necessary. There should always be enough sauce at the bottom of the tagine so the meat doesn't burn.
Once the chicken is done, taste the sauce and adjust the seasoning.
Add the lemon peel and olives to the tagine. Continue cooking, uncovered, for a few minutes, until the sauce slightly thickens.
Serve the tagine hot with crusty bread.