Pour the oil into a large frying pan and heat it. You don't need to completely submerge the churros, but ensure there's enough oil for them to fry evenly. While the oil heats, fill a piping bag fitted with a star tip with about half of the dough – it's easier to manage in smaller batches.
Test the oil by dropping a tiny piece of dough into it. When it turns a deep brown quickly, the oil is ready. Carefully pipe the dough directly into the hot oil, cutting it to your desired length with a fork (it's surprisingly effective). Don't overcrowd the pan; leave enough space for the churros to fry properly.
Fry the churros for about 2 minutes, or until they reach a consistent golden color. If they're browning unevenly, slightly reduce the heat. Once fried, use tongs or a slotted spoon to transfer them to a paper towel-lined plate to drain any excess oil.
While the churros are still warm, roll each one generously in cinnamon sugar until fully coated.