Slice the Asian eggplants (if using) lengthwise into quarters, keeping the stem intact so that it holds the eggplant together. Heat the oil in a wok until almost smoking, then turn the heat down to medium and fry the eggplants well, turning occasionally. Do not burn. Transfer the eggplants to a baking dish. Cook under a preheated medium broiler for 20 minutes, turning the eggplants halfway through.
Chop the mint finely, and the cilantro leaves coarsely. Set aside. (If you have roots on your cilantro stalks, wash them well, chop them finely, and add them to the mortar to be ground into the nuoc cham sauce.)
To assemble, place the eggplants in a serving dish while warm, top with the mint and cilantro, and dress with the nuoc cham. Finally, scatter the dish with the cashews to serve.
Nuoc cham is a Vietnamese dipping sauce, commonly served with noodle salads, egg rolls, summer rolls, and banh xeo (a crêpe-like pancake stuffed with bean sprouts and protein). Essentially, this sauce should be made with the component parts as you prefer. So keep tasting and adding them according to your taste, because you might like it more sour, more sweet, or more or less spicy. This is how I like mine.
Peel the garlic clove and crush with the sugar using a mortar and pestle until it is a smooth paste. Seed the chile, chop it coarsely, and then add it to the mortar and give it a good pounding. Add the lime juice and mix well. Add 1 tablespoon of the fish sauce and taste. Add 1 tablespoon water and taste. Keep doing this until you have the desired piquancy or pungency. Remember that you can always add but you can’t take away.