Cube your bread and place it in the slow cooker.
Add the eggs, milk, cinnamon, vanilla extract, Nutella, and salt to a bowl and whisk to combine.
Pour over the challah bread in the slow cooker.
Mix so that all of the bread is saturated with the mixture.
Cover and cook on HIGH for 2 hours. (NOTE: depending on the size and heat of your slow cooker, this time may have to be adjusted. Check every hour hour, mixing for even cooking)
When there are about 15 minutes left on the slow cooker, slice your bananas and add to a bowl.
Add the brown sugar and mix to combine.
Add the butter to a saute pan over medium high heat. Add the banana slices to the pan (you may have to work in batches) and cook for about 2 minutes on each side or until the bananas have browned slightly.
Scoop out the French Toast mixture and top with a scoop of the bananas. Add a dollop of Nutella if desired.