Our take on som tom o, Thai pomelo salad, uses grapefruit as a stand-in for the highly seasonal pomelo. Traditional versions include dried shrimp as a flavoring, but we use fresh shrimp and include enough to turn the salad into a light main dish. To segment grapefruit, cut off the top and bottom and set the fruit on a cut end. Working from top to bottom and following the fruit's contour, cut away the peel and white pith. Slide the knife along each side of the membranes separating the segments. If your roasted cashews are only lightly browned, toast them in a dry skillet for a few minutes to bring out their flavor and crisp them.