Prep the eggplant: Arrange the eggplant rounds on two sheet pans.
Sprinkle both sides with kosher salt. Let sit for 20–30 minutes to draw out moisture and bitterness. Pat dry with paper towels.
Preheat and set up: Heat the oven to 425°F (220°C).
Lightly oil the sheet pans or line with parchment. Grease a 9x13-inch baking dish.
Roast the eggplant: Brush both sides of the eggplant with olive oil and season with pepper. Roast for 20–25 minutes, flipping halfway, until soft and lightly browned.
Reduce oven temperature to 375°F (190°C).
Mix the topping: In a bowl, combine breadcrumbs, Parmesan, oregano, red pepper flakes, and a drizzle of olive oil. If using the egg, mix it in to help the topping clump and crisp.
Layer the bake: Spread 1/2 cup marinara in the baking dish. Add a single layer of eggplant.
Spoon over more marinara, sprinkle with mozzarella, and scatter some basil. Repeat layers until all eggplant is used, finishing with a light layer of sauce and mozzarella on top.
Add the crunch: Sprinkle the breadcrumb-Parmesan mixture evenly over the top. Press gently so it adheres.
Bake: Bake at 375°F (190°C) for 25–30 minutes, until the cheese is bubbling and the topping is golden.
Rest and serve: Let the bake rest for 10–15 minutes to set.
Garnish with fresh basil and extra Parmesan. Serve warm.