Cream together the vegan margarine and the sugar in a mixing bowl until light and creamy.
Add the orange zest, ginger or lemon zest, depending on which flavour of biscuit you are making, and stir in the flour to form a dough.
Using your hands, bring the dough together into a smooth bowl and wrap in cling film. Refrigerate for 40 minutes to allow the margarine to firm up a little.
Preheat the oven to 160C/140C Fan/Gas 3 and line two baking trays with baking parchment.
Generously flour a clean work surface and roll out the dough to about 4mm/⅛in thickness. Using a medium cutter, cut the biscuits into rounds, gently kneading any scraps back into a ball and rolling them out again to yield more biscuits.
Bake the biscuits for 12–14 minutes, or until they are just golden-brown.
Slide the biscuits onto a cooling rack to cool while you make the icing.
Stir together the icing sugar and orange juice; icing sugar and lemon juice; or the icing sugar, rosewater and water. Using the back of the spoon, smooth the icing over the surface of each biscuit, once cool.
Sprinkle the top of the biscuits with a couple of dried rose petals, if using, and leave the icing to set before storing in an airtight tin.