Preheat fan oven to 180°C. In a bowl mix flour, baking powder, salt, cinnamon, nutmeg, ground ginger, cocoa powder and crushed ginger biscuits and set aside.
In a separate bowl, whisk sugar and butter until pale and fluffy. Whisk in oil, vanilla, eggs (one at a time) and buttermilk.
Fold in the flour mixture and mix gently. Divide mixture between 12 cupcake cases and bake at 180°C for 15 minutes.
Leave to cool for at least 10 minutes. For the cream cheese frosting mix ingredients with a hand mixer until light and fluffy and pipe using a piping bag or a plastic bag. Decorate with a mini gingerbread man.