In a medium bowl mix together the vegetable oil, sugar and eggs. Stir in yoghurt and orange zest. Combine the flour and baking powder; stir into the mixture just until blended. Pour the dough into a greased 20x30cm baking tin.
Bake for 30 minutes in the preheated oven or until a knife inserted into the cake comes out clean. Poke holes in the cake with a knife and pour the juice from the oranges over the cake slowly until it has all been absorbed.
Cut the liquorice into small triangles and arrange to make a jack o lantern face.