Why are banana prawns called banana prawns?

Because its a banana in a shape of a prawn. Banana prawns are well suited to Asian style cooking and generally serve as part of meal rather than served alone. The sweetness of their flesh and thin shell goes well with spicy flavours.
I tend to leave the heads, shells on and just clean the guts.
A quick fry in a very hot pan with a bit of oil till they turn pink.  Add aromatics like garlic and chillies. Then bit of sugar and then some light soya. Lastly stir in chopped green shallots (especially the white parts) and chinese coriander .
This is one of our favourite quick stir fry.  The flavour of the dish changes depending what you add as flavouring. Try chinese plum sauce and if you do use it..omit the sugar.