How to Make It
Preheat grill to very high (500°F and up). Peel eggplants, leaving stems intact. Season all over with salt and pepper, and place on a small baking sheet. Let stand at room temperature at least 5 minutes or up to 30 minutes; pat dry with paper towels.
Whisk together 6 tablespoons hot water and sugar in a small bowl until sugar dissolves. Whisk in fish sauce, lime juice, ginger, garlic, and chile. Add lemongrass, and, if desired, lime leaf.
Place eggplants on oiled grates; grill, covered, turning occasionally, until slightly charred and very tender when pierced with a knife, about 15 minutes. Cut eggplants in half lengthwise (do not cut all the way through).
Divide eggplants among 4 large shallow bowls. Stuff eggplants evenly with herbs, radishes, and red onion. Drizzle 2 tablespoons dressing over each stuffed eggplant. Top evenly with peanuts, scallions, fried shallots, and fried garlic. Sprinkle with additional herbs. Serve warm or at room temperature.
Alternatively, eggplant can be cooked in a skillet. Working in batches, sear the eggplants in vegetable oil in a cast-iron skillet over medium-high until browned on all sides and tender.