Put the cake mix in a bowl and stir in the ginger and cinnamon. Add the oil, treacle and eggs and beat with a wooden spoon to make a firm dough. Roll out the dough between 2 large sheets of baking paper to 7mm thickness (about 30cm square). Slide onto a large baking sheet and chill in the fridge for 30 minutes.
Preheat the oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Line 2 large baking sheets with baking paper.
Peel off the top sheet of baking paper from the dough and using 5cm star and heart shaped cookie cutters, stamp out 10 stars and 10 hearts. Place, well-spaced apart, on the baking sheets. Gather the remaining dough pieces into a ball then divide, roll and flatten into 10 x 5cm diameter rounds. Place on the baking sheets.
Bake for 11-13 minutes until pale golden and set. Leave on the trays for 5 minutes, then transfer to a wire rack and leave to cool completely.
Place the chocolate icing in a microwave-proof bowl and heat on High for 20-30 seconds or until melted. Stir until smooth. Dip half of each cookie into the icing to coat (see Tip) and place on a wire rack. Chill in the fridge for 15 minutes until set.
Place the vanilla icing in a microwave-proof bowl and heat on High for 5 seconds until melted. Stir until smooth, then spoon into a disposable piping bag fitted with a fine writing nozzle. Pipe zig-zag lines of icing over each cookie. Leave to set. Eat immediately or store in an airtight container in a cool place for up to 1 day.