Using garbanzo flour instead of canned garbanzo beans
For this specific recipe, you may be able to get away with this substitution, since what you're making is a bread, but also because it's a bread there's less room for error than in many dishes. Rather than try to substitute in this specific recipe, I'd look for another recipe for banana bread made with garbanzo bean flour - a cursory google found many - and alter sweeteners and spices as needed or desired to get closer to this one.  (Most artificial sweeteners have established, standardized subsitutions for sugar, so that's going to be an easier change than using chickpea flour in place of canned garbanzos.)