Tamarind brings not only sourness but also sweetness to this crunchy salad. I like to buy the solid blocks of tamarind paste found at Asian supermarkets, tear off a chunk and soak it in boiling water before passing it through a sieve to remove the seeds. You’ll get better flavour this way, but the more readily available (and easier!) tamarind puree can be used instead, I won’t tell. Make sure you mix and dress this salad right before you plan to eat, otherwise you risk the crunchy bits going soggy.