Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper and lightly brush it with oil. Wash the eggplants, dry them thoroughly, and cut them into bite-sized cubes or thick wedges.
- Prepare the eggplant.Place the cut eggplant in a large bowl and sprinkle with salt and black pepper. Toss gently, then let it sit for about 10 minutes if you have time. Pat away any moisture that collects on the surface.
- Coat with cornstarch.Add the cornstarch to the eggplant and toss until each piece has a light, even coating. Shake off any excess powder to prevent a chalky texture.
- Arrange and oil the pieces.Spread the eggplant in a single layer on the prepared baking sheet. Drizzle with the neutral oil and turn the pieces so they are lightly coated. Leave space between them to help the edges crisp.
- Bake until golden.Roast for 20–25 minutes, turning the pieces halfway through. Continue cooking until the eggplant is tender inside and golden around the edges. Cooking time may vary depending on the size of the pieces.
- Mix the miso glaze.While the eggplant bakes, whisk together the miso paste, soy sauce, honey or maple syrup, rice vinegar, sesame oil, garlic, and ginger in a small bowl. Add 1–2 tablespoons of water until the glaze is smooth and easy to brush over the eggplant.
- Heat the glaze.Pour the mixture into a small saucepan and warm over low heat for 1–2 minutes, stirring constantly. Avoid boiling it vigorously, as the sugars can burn and the glaze may become too thick.
- Glaze the eggplant.Transfer the roasted eggplant to a large bowl and gently toss it with enough glaze to coat each piece. Reserve a little sauce for serving if desired.
- Caramelize briefly.Return the glazed eggplant to the baking sheet and roast for another 3–5 minutes. Watch closely, since the honey or maple syrup can brown quickly. The glaze should look glossy and lightly caramelized.
- Garnish and serve.Sprinkle the eggplant with sesame seeds, sliced green onions, and chili flakes if you like a little heat. Serve immediately while the edges are still crisp.