Preheat the oven to 400 F and arrange the walnuts on a baking sheet in a single layer. Toast for 7 to 10 minutes, mixing once half way though. Allow to cool. Chop and set aside.
In a large skillet over medium heat, melt the butter. Add the oats and toast until golden and fragrant, about 2 minutes, stirring as needed. Transfer to a large slow cooker.
Pour in the water, bananas, walnuts (though, I saved a few for topping), brown sugar, salt, and cinnamon. Stir, cover and let cook for 4 to 6 hours on low.
If serving right out of the crock pot - let sit for 10 minutes. Store up to 4 days in containers in the fridge.
Notes
Slow Cooker Revolution I bumped up the cinnamon on this recipe to 1/2 teas. Also, since I store these in individual containers for the week, you can reheat with a little added sugar and milk if needed.