Set a small saucepan over medium heat. Whisk together the water, sugar, salt and oil. Bring the mixture to a boil then remove it from the heat. Stir in the flour, mixing until it comes together and forms a dough ball.
Heat enough oil in a deep, heavy-bottomed pot set over medium-high heat until it reaches 375ºF. Line a cookie sheet or a plate with kitchen towels.
Transfer the prepared churro dough into a pastry bag fitted with a large star tip (see notes).
Pipe the dough over the pot of oil to a length of about 4 inches, then using scissors or a sharp knife, cut it so it releases into the oil.
Alternately, you can pipe the dough onto a parchment lined cookie sheet while you oil is heating up and then fry them.
Fry two to three churros into the oil at a time. Make sure your oil is at the right temperature, otherwise the churros might brown too quickly from the outside and not get cooked through.
Use a slotted spoon to transfer the churros to the kitchen towel-lined cookie sheet to drain for about a minute or 2.
While the churros are still hot, transfer them to the shallow bowl containing the cinnamon-sugar mixture and roll them around until completely coated.
Use up the remaining dough, frying and coating the churros as explained above.