Collect the juiciest, ripest tomatoes you can find for this salad (the sweeter and fruitier, the better), which is amplified by an herby, piquant dressing. Start with cilantro, scallions, and Thai basil; perilla leaves lend a grassy, aniseed note. You can find them at Asian grocery stores or greenmarkets, but, if they’re unavailable, substitute shiso or mint. Tamarind is very sour, too tart to enjoy on its own, but paired with a sweetener, such as maple syrup, honey or brown sugar, it sings…