Smash inside layers of bottom half of lemongrass (the stalk part) and mince.  Put the oil in a wok or skillet over maximum heat. Add the ginger, garlic and lemongrass and give a quick stir. Immediately add the eggplant and ½ teaspoon of kosher salt. Stir-fry for a minute or so. Add ¼ cup of water and cover. Cook, checking and stirring every 30 seconds or so, until the eggplant is just about completely tender. You may need more water.  Remove the lid and add the mushrooms, onion, chili and basil. Stir fry for about 1 minute until the mushrooms are somewhat tender.  Garnish with basil.