01 - Preheat oven to 400°F. Line two baking sheets with parchment paper.
02 - Arrange eggplant slices on baking sheets. Brush with olive oil and sprinkle lightly with salt. Roast for 20 minutes, flipping halfway through, until slices are tender and lightly golden. Lower oven temperature to 375°F.
03 - Heat olive oil in a large skillet over medium. Sauté onion until translucent, about 4 minutes. Add garlic and cook 1 minute. Stir in spinach and 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 until well blended.
05 - Spread 1/2 cup marinara sauce over bottom of a 9x13-inch baking dish. Add a layer of roasted eggplant, followed by lasagna noodles.
06 - Spread one-third of ricotta mixture over noodles. Sprinkle with 2/3 cup mozzarella and spoon 3/4 cup marinara sauce on top.
07 - Repeat layering with remaining eggplant, noodles, ricotta filling, mozzarella, and marinara sauce two more times. Finish with sauce and top with remaining mozzarella and Parmesan.
08 - Cover dish tightly with aluminum foil. Bake for 30 minutes. Remove foil and bake for additional 15 minutes, until cheese is bubbly and golden.
09 - Allow dish to rest for 10 minutes before slicing. Garnish with fresh basil, if desired.