We had that for years... if something broke while eating it, then the whole thing is gone. I used to get so angry and frustrated at her... then I just gave up... She has had the issue recently with bread having a hole in it...
Yes we have the same with bread! I have to go through the loaf to find two pieces with no holes.... not easy when I often make my own!

So, from this I would guess the best thing to do is physically show him, before it's an issue, a whole banana saying "whole banana", and then show him what it looks like when you break in half saying, "half a banana", and then show him how it fits together, and go from there.
Thanks! I'll try that

He seems ok if he watches (and helps) me cut it up, it's just when it breaks. Sandwiches are painful.... they have to be equal pieces when cut or he won't touch it.