Preheat the oven to 425°F and line three large baking sheets with parchment paper. Arrange the eggplant planks in a single layer on clean kitchen towels and sprinkle with salt. Set aside for 20 minutes to draw moisture out of the eggplant.

Pat the eggplant dry and transfer to the prepared baking sheets. Drizzle generously with olive oil, toss to coat, and arrange in a single layer on the baking sheets. Roast for 20 to 25 minutes, or until tender and golden brown, flipping the eggplant and rotating the pans halfway through.

Meanwhile, make the filling: In a large bowl, stir together the ricotta, egg, Parmesan, garlic, oregano, lemon zest, salt, and pepper.

Brush a 9x13-inch or similar baking dish with olive oil and spread 1/2 cup of the marinara sauce on the bottom. Cover with a layer of the roasted eggplant slices, then top with half the ricotta mixture and dot with another 1/2 cup of the marinara. Repeat with another layer of eggplant, the remaining ricotta mixture, and the remaining 1/2 cup marinara. Top with a final layer of eggplant, then sprinkle the mozzarella and Parmesan cheeses on top.

Bake for 30 minutes, or until the cheese on top is browned and bubbling. Let stand for 30 minutes. Sprinkle with red pepper flakes and garnish with fresh basil. Slice and serve.