1) Place zest, sugar and cinnamon in a paper bag and shake to combine.
2) Place oil in a deep pan until it comes about halfway up the side of the pan. Heat oil to 180 degrees C.
3) Slice biscuit dough in quarters and roll into balls to form 24 doughnut holes. Working in batches, place doughnut holes in hot oil and fry until golden, about 6 to 8 minutes.
4) Transfer the hot doughnuts to the paper bag and shake to coat with orange sugar. Serve immediately.