Preheat the oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil and spray it with cooking spray.

Cut each slice of bread into three sticks. Whisk together milk, egg, vanilla extract, and cinnamon in a large shallow dish. Dip each bread stick in the egg mixture quickly to avoid soaking the bread, yet coating it on all sides; shake off excess. Arrange bread sticks on the prepared baking sheet without them touching.

Bake in the preheated oven for 8 minutes, flip them, spray lightly with cooking spray, and return to the oven until cooked through and golden brown, about 8 more minutes.

Meanwhile, whisk together hazelnut spread, half-and-half, cocoa powder, corn syrup, and salt in a small saucepan on medium-low heat. Bring to a boil and immediately remove pan from the heat, whisking until smooth.

Remove French toast sticks from the oven and serve warm with the chocolate dipping sauce.