In a bowl, mix the orange juice, the sugar, and the tahini. Add the water and continue mixing.
In a separate bowl, mix the rest of the ingredients. Add them to the tahini mixture and mix well. Transfer the cake mixture into a greased cake mould and bake at 170 for 40-45 minutes.
In a water bath, melt the chocolate. Remove the cake from the mould, pour the chocoloate over it, sprinkle with walknuts and serve.