Preheat the oven to 400F (200°C). Grease a large baking sheet and set aside, then set a 9×13” casserole dish aside. Slice the eggplant into thin slices; I like to lay them out in the baking dish before proceeding with the recipe, so I can have a good idea of how things will fit and make assembly easier later on. For this recipe I made 6 stacks of 3 eggplant slices in my baking dish.
Add the kosher salt and 4 cups of water to large bowl or pot (I find using a pot with tall sides is easiest). Whisk the salt into the water until it has completely dissolved, then add your sliced eggplant to the water. Cover with an additional 4 cups of water, adding more as necessary. The eggplant will float to the top, so I like to weigh it down with a smaller pot lid or heavy plate so it is completely submerged. Let soak for 10 minutes (Note: I make my batter & breadcrumbs during this time).
In the meantime whisk the oil, soy milk, cornstarch, and salt together in a small bowl; set aside.
Add the panko breadcrumbs to a medium bowl with a wide base. Add the dairy-free parmesan, oregano, thyme, chili flakes, paprika, salt, and black pepper to the bowl and mix well. Take half of the breadcrumb mixture out of the bowl and set aside; this will help prevent the breadcrumbs from getting soggy later on.
Drain the eggplant and transfer it to a clean kitchen towel. Pat dry.
Use your left hand to dip both sides of one eggplant slice into the wet batter. Shake any excess batter off, then transfer to the breadcrumb bowl. Use your right hand or a spoon to spread breadcrumbs over the top of the eggplant and lightly press down. Shake off any excess crumbs, then transfer to the prepared baking sheet. Repeat with the remaining eggplant slices, adding the second half of the breadcrumb mixture to the bowl once you are almost out of the first half.
Generously spray the eggplant sliced with cooking oil, or drizzle with olive oil. Bake on the top rack of the oven for 20 minutes, until the breadcrumbs are golden. Remove from the oven and increase the oven temperature to 415F.
Use a spatula to spread 1 cup of marinara sauce across the bottom of your baking dish, then add 1 layer of the baked eggplant sliced. Dollop 3/4 cup of marinara over the eggplant slices and spread evenly, then sprinkle with roughly 1/3 of the cheese (or half, if you are only doing 2 layers). Repeat this process with the second layer of eggplant. Repeat for the top layer of eggplant, then dollop 1 cup of sauce over the eggplant and top with the remaining cheese.
Bake in the middle rack of the oven for 20 minutes, until the sauce is bubbly and the cheese has melted.
Sprinkle the casserole with fresh basil and serve immediately. Store any leftovers in an airtight container in the refrigerator for up to 5 days. Leftovers are best reheated in the oven or toaster oven for a crispier eggplant parmesan, but you can also use the microwave if you don’t mind it being a bit softer.