You could, but I'd more likely use the word 'crushed.'
For whatever reason (I don't know exactly why) I usually say something is squashed if it has some liquid at all, and 'crushed' if it is more of a dry thing. (AmE perspective, other dialects of English may differ - this is only my perspective.)
I would 'crush' a ping pong ball.
If I stepped on a jelly fish, I would say that it 'squished' under my foot.