Preheat the oven to 375°F (190°C). Peel the eggplant and slice into 1 centimeter rounds. Arrange the slices in a single layer on a tray and sprinkle with salt.
After 15 minutes, once the eggplant slices have excreted their bitter, gross tasting liquid, rinse and drain the slices in a colander and let them drip dry.
Meanwhile, prepare the batter. In a large bowl, whisk together the plant-based milk, apple cider vinegar, bouillon paste, flour, and salt. Whisk until smooth and completely free of lumps.
In a separate shallow dish, combine the panko, flour, oregano, black pepper, and salt.
Working with 1 slice at a time, dip the eggplant into the batter, allowing any excess to drip back into the bowl. Transfer to the breadcrumb mixture and coat evenly on both sides, pressing gently so the crumbs adhere. Place the breaded slices on a clean tray.
Pour the frying oil into a wide, heavy-bottomed Dutch oven to a depth of 1 inch (2.5 cm). Place the pot over medium-high heat. After 3 minutes, test the oil by adding a small pinch of breadcrumbs; they should sizzle steadily without darkening immediately. Carefully add several eggplant slices in a single layer without overcrowding. Fry for 3 minutes per side over medium-high heat until deeply golden. Transfer to a rack to drip dry. Repeat with the remaining slices, adding oil as needed and maintaining steady heat. Prepare the cheese sauce. Place a saucepan over medium heat and add the olive oil. After 60 seconds, add the minced garlic and cook for 60 seconds, stirring constantly so it does not darken. Add the tapioca starch, flour, and nutritional yeast. Stir continuously for 2 minutes to form a smooth paste. Gradually whisk in the plant-based milk until smooth. Cook over medium heat for 4 minutes, stirring constantly, until thickened. Add the vegan mozzarella, rice vinegar, mustard, and salt. Continue stirring until the cheese melts and the sauce is smooth. Remove from the heat.
Spread a thin layer of marinara in the bottom of a baking dish. Arrange a single layer of fried eggplant over the sauce. Spoon additional marinara over the eggplant, followed by a layer of cheese sauce. Repeat the layering until all components are used, finishing with cheese sauce on top.
On the top layer, swirl together the sauce and cheese using the back of a spoon. Cover the pan in foil, tenting the foil up in the center a little so that it isn’t in direct contact with the top of the eggplant parm.
Bake on the center rack for 25 minutes at 375°F (190°C).
Remove the foil and continue to bake for 15 minutes until bubbling and lightly golden on top. Let rest for 10 minutes before cutting.
Garnish with fresh basil leaves and grated vegan parmesan before serving.