This is a recipe for a classic moroccan fish mqualli tagine with potatoes, tomatoes, and peppers. Traditionally, the ingredients are layered in a tagine or deep skillet, then cooked over a fire or on the stove. In the north of morocco, fish stews such as this one are prepared in tagras, round or oval clay casseroles similar to tagines, but without the conical top. Mqualli is a term which refers to sauces made with ginger, saffron, and oil. Here, however, the additional zesty flavor comes from fresh or preserved lemons, olives and a moroccan marinade called chermoula. Any firm, thick fish can be usedcut up or wholebut slices of conger eel work best because there are fewer bones to deal with at the table. Swordfish, dorado, large whole whiting and sea bass are other good choices.