Preheat the oven to 375°F (190°C) degrees.
In a bowl combine flour, cocoa powder, and baking powder. Set aside.
In a different bowl, add the water and oil. Pour in the sugar and whisk until it dissolves.
Pour the liquid into the dry ingredients and work to form a smooth dough.
Roll out the dough on a lightly floured surface to about 1/4 inch (6mm) thick.6. Cut out the cookies and arrange them on a parchment-lined baking sheet.
Bake for about 12 minutes and allow to cool down completely before removing to wire racks.
When you’re ready to decorate, make the icing: Mix the lemon juice and oat milk with the confectioners' sugar. The icing should be thick but pourable and should hold its shape.
Transfer the icing to a decorating pen (or a piping bag with a fine nozzle) and decorate the cookies as you like.
Leave the cookies to dry flat for at least 2 hours before storing in an airtight container.