Cut the eggplants in half lengthwise, then score each eggplant half with a diamond pattern, making sure not to cut right through to the skin.
In a bowl, whisk together the miso, sesame oil, maple syrup, warm water, ginger and garlic powder to make a marinade. Pour into a roasting pan and lay the eggplants, scored side down, in the marinade. Leave to marinate for 1–2 hours.
Preheat the oven to 400°F (200°C). Cover the roasting pan with foil and bake the eggplants for 30–35 minutes, until very tender. Remove from the oven, take off the foil and flip the eggplants over, then spoon some of the cooking juices from the pan over the eggplants. Sprinkle with a generous layer of sesame seeds, then return to the oven, uncovered, for another 5 minutes to toast the sesame seeds and give them a lovely crunch.
Serve garnished with scallion and chili slices. If you like, you can pour any remaining cooking juices into a small bowl and serve alongside the eggplant.