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Exactly, banana makes it sticky enough to hold it together and also it adds sweetness. I also added dried fruits and as I like it more semi-sweet I didn't add any sugar. Agave syrup or honey would be great in this recipe if you like to make it sweeter, it would also make it more sticky.

I'd probably skip the added sugar myself as well.

I really don't miss it in the granola, it's so much better without. It's also not easy to find at the store the one without sugar.