Preheat oven to 400°F and place one rack in the middle of the oven and one rack in the upper third. Line two baking sheets with a cooling rack. Place eggplant slices on racks and season generously with salt. Let sit 15 minutes, then dab excess moisture with a paper towel. Flip eggplant slices and repeat.

In a large skillet, heat oil over medium heat. Add onion and cook until softened and translucent, 5 minutes. Add garlic and Italian seasoning, cooking until fragrant, 1 minute. Season to taste with salt and pepper. Add marinara sauce and ¼ cup fresh basil, stirring to combine. Simmer until warmed through, 3 minutes. Remove from heat.

In a 13x9 baking dish, pour ⅓ marinara on bottom of pan. Top with ⅓ eggplant slices, then ⅓ ricotta mixture, and 1 cup shredded mozzarella cheese. Repeat this sequence an additional 2 times, finishing off the final sprinkling of mozzarella cheese with remaining ¼ cup Parmesan and black pepper. Lightly grease a sheet of foil and cover lasagna, greased side down, with foil. Bake on middle rack until eggplant is softened and cheese is melted, 30 minutes. Remove foil.