Once upon a time, I was peeling a banana in a dim and very dry room, and I'm pretty sure I saw a spark, perhaps caused by the same phenomenon.

Very cool! From cursory research it seems like many salicylates produce triboluminescence (I don't know why), and some people online with special dietary needs say that bananas are high in salicylates (though it seems controversial). So that would be my hypothesis.

I'm gunnuh try crushing an aspirin (acetylsalicylic acid) and see what happens. (ETA: My headache pills that have aspirin, acetaminophen, and caffeine, along with whatever binders, did not produce any light that my camera detected. That's the only aspirin I have and I'm only willing to sacrifice one of them. Oh well!)

ETA2: Wasn't able to get it to work by peeling a banana, crushing the inside, or crushing the peel, but I don't doubt it happened. Bananas probably vary a great deal. Thanks for the fun diversion, I haven't done an experiment like this in years.