I might have just the recipe for you! Below is the video for the recipe I made for Charlie's birthday cake. It has a bit of carrot, pumpkin seeds, oats, a bit of walnut and 4 raisins. You could substitute the raisins for a bit of apple. Banana might make it go a bit mushy - and you could substitue the carrot for pumpkin possibly. It's very easy and all the instructions are there.
It comes out like a nice looking cake - a bit tasteless for humans as no sugar, but Charlie liked it
https://www.youtube.com/watch?v=ZGSPALpaDBQ
A little bit of apple or banana occasionally is ok for Syrians but probably not for dwarf hammies.