Heat oven according to your canned croissant or biscuit roll instructions.
Spray baking sheet with a non-stick cooking spray
Open croissants. Spoon and spread Nutella in the middle of the dough. Avoid putting it on the edges or it will spill out during cooking. If you're using biscuit dough flatten it as much as you can before spreading Nutella.
Slice or dice half a banana and put it on top of Nutella. Alternatively, you can just put half a banana in the middle without slicing.
Roll up the dough and use your fingers to pinch closed on the edges.