Mix flour, baking powder and salt in a bowl. Add oil and water and mix until just combined, until it forms a thick batter.
Transfer dough into a piping bag with a star tip nozzle. Let cool.
Line a baking tray with greaseproof paper and pipe small circles of churro batter, slightly bigger than the diameter of your Nutella ball. Top each with a Nutella ball and then pipe, from the bottom, around each Nutella ball, so you have encased the Nutella ball in churro dough.
Place into the freezer for 4 hours.
When ready to cook, heat oil over medium-high heat in a wok or small, deep saucepan.
Fry 3 to 4 churro bombs per batch for about 3 to 4 minutes or until golden, turning occasionally.
Remove onto a paper towel-lined plate to drain. Roll in cinnamon sugar and leave to cool for 5 minutes before eating.