To make the Nutella chocolate sauce, combine chocolate and milk in a saucepan on low heat until smooth. Remove from the heat and stir in Nutella. Set aside.
To make the churro bites, combine cinnamon and sugar in a bowl. Cut the bread into 1-inch cubes. Dip each bread cube in melted butter, then coat in cinnamon-sugar mixture.
Preheat the air fryer to 350°F (175°C). Cook the bread cubes for 6-8 minutes, flipping halfway through. Serve churro bites with Nutella chocolate sauce for dipping. Enjoy!