Preheat the oven to 180ºC, fan 160ºC, gas 4. Roll out the gingerbread dough to the thickness of a pound coin. Stamp out Halloween shapes using the cookie cutters – there's a witch, pumpkin, ghost and bat - and put on a large baking tray lined with baking parchment. Bake for 8-10 minutes, then leave to cool on a wire rack.
Make the icing: put the water, lemon juice and icing sugar into a bowl. Mix well, until completely smooth. It should be thick enough to coat the back of a spoon - if needed, add more icing sugar to thicken, or a little warm water to thin.
Divide the icing between 3 bowls, add the orange food colouring to one bowl and the black to another and mix until you have an even colour.
Spread the icing evenly over the biscuits, leaving a neat border – you could use the back of a spoon or for a really neat edge, use a disposable piping bag fitted with a small round nozzle. Once the icing has set, decorate with the writing icing.