This traditional chicken dish from the Casamance region of Senegal is one of the most famous African recipes and is found in Senegalese restaurants the world over. For best results let the chicken marinate overnight; in Africa, this is essential to tenderize the sometimes tougher African fowl. It is also very good when made with fish. For the simplest yassa, make the marinade from just oil, lemon juice, onions, and a little mustard.