01 - Preheat oven to 400°F. Line two baking sheets with parchment paper.
02 - Arrange eggplant slices on the prepared baking sheets, brush lightly with olive oil, sprinkle with salt, and roast for 20 minutes, flipping halfway through until tender and lightly golden. Lower oven to 375°F.
03 - In a large skillet over medium heat, add a splash of olive oil. Sauté onion until translucent, approximately 4 minutes. Add garlic and cook for 1 minute more. Stir in spinach; cook until wilted. Remove from heat and let cool slightly.
04 - In a mixing bowl, combine ricotta cheese, egg, sautéed spinach mixture, 1/4 cup Parmesan, oregano, basil, salt, and pepper. Mix thoroughly.
05 - Spread 1/2 cup marinara sauce in the bottom of a 9x13-inch baking dish. Layer roasted eggplant slices, followed by lasagna noodles.
06 - Spread one-third of the ricotta mixture over noodles, sprinkle with 2/3 cup mozzarella, then spoon over 3/4 cup marinara sauce.
07 - Repeat layering with eggplant, noodles, ricotta mixture, mozzarella, and sauce two more times, finishing with a final layer of sauce and remaining mozzarella and Parmesan on top.
08 - Cover baking dish with aluminum foil and bake for 30 minutes at 375°F.
09 - Remove foil and bake an additional 15 minutes until cheese is bubbling and golden.
10 - Allow to rest for 10 minutes before slicing. Garnish with fresh basil if desired.