Combine all ingredients except the chocolate chips for the cake in a large bowl.
Mix to get out any lumps.
Add the chocolate chips and stir through.
Pour into a 20 by 20 cm square cake tin.
Bake for 40 minutes at 180 degrees. Check with a skewer for doneness- if it comes out clear you're good to go!
Allow cake to cool completely.
Icing
Melt the cooking chocolate using your preferred method.
Spread over the cake.
Sprinkle with the orange zest and serve when the icing has set.
Notes
freezer friendly: this cake is great for freezing, even when iced. I cut into squares before freezing so that I can grab pieces and pop them in the lunchbox.