What the Hell Is It?

What is it?

Ransacking a southern Mexican grocery in East Elmhurst recently, filled with all sorts of unfamiliar fresh herbs and packaged goods, I ran across this odd fruit (or vegetable). The shopkeeper had a name for it in an Indian dialect — which I despaired of transliterating into English — but no English or Spanish moniker. It has spines like a cactus, but it’s a little softer, and shiny and dark green underneath. If you know what it is, please tell me!