we had too many bananas to use, so we froze some. Mrs Piper wants to make some banana muffins - do we thaw them first, or can we just mash them up as is?
After they thaw, the will squeeze like paste out of the skin. Basically, it will be semi-liquid pulp. Convenient, that. 
In other words – thaw, no mash.
If you’re baking something with leavening (banana muffins, quick bread, yeast bread), it will probably be best if you leave them thaw. Your muffins will raise a bit higher.
Personally, I like to begin baking with all ingrediants at room temp. YMMV.
The only way I’d leave them frozen is if I was going to eat them straight, as they’re rather good that way.
I don’t know. How hot are you?