Peel the eggplant skin in stripes (you don't have to peel all of the skin off). Cut each eggplant in half vertically. Make slits over the surface but don't cut through the skin. Sprinkle salt over the eggplant surfaces and let them sweat for at least 10 minutes.
Meanwhile, mix together the corn starch and water to make a slurry. Set aside.
Make the miso glaze by combining miso, sake, mirin, dashi, and maple syrup in a small saucepan over medium low heat. Stir continuously. When the miso mixture starts boiling, add the corn starch slurry and continue to mix until the glaze has thickened. Turn off the heat and let sit while you prepare the eggplants.
Wipe off the liquid that comes out on the surface of the eggplants. Spray/brush oil over the surface of the eggplants. Microwave until soft, about 5 minutes. Flip halfway through.
Heat a pan over medium heat. Brush oil over the cut sides of the eggplants. Place the eggplants cut side down on the frying pan and cook until soft and browned. Brush remaining oil on the other side of the eggplants and flip eggplants over. Cook till browned and soft. Pour miso glaze over top and serve while still warm.
Notes
*If using dashi powder, mix 1/2 tsp dashi with 1/2 cup water.