The really chocolately banana bread I made hid the taste somewhat, but that recipe had chocolate chips and sugar, so probably fewer bananas.
They're one of the sweetest fruits. Carrots and apples are probably next in line if he likes those better, and maybe white grape juice though I haven't seen it used much. Applesauce cake rarely tastes like apples, so maybe a spice cake with that if he doesn't like carrot cake? There are probably chocolate versions. I've made pumpkin chocolate cake where it was hard to identify the pumpkin, but that was with boxed cake mix, so full sugar.
I know there's chocolate avocado frosting, but I don't know how it's sweetened.