Preheat oven to 425 degrees. Line 2 to 3 sheet pans with parchment paper and arrange the eggplant pieces in an even layer. Brush or drizzle all over with olive oil and sprinkle with Italian seasoning, and season with salt and pepper. Roast in the oven for 20 to 25 minutes, until tender and lightly browned.
Bring a pot of water to a boil and cook lasagna noodles according to package instructions. When finished, drain and set aside. Feel free to drizzle with olive oil so the noodles don't stick together.
While the eggplant is in the oven, make the ricotta filling: Place the spinach in a medium bowl. Add the ricotta, ⅓ cup Parmesan, egg, lemon zest, red-pepper flakes, salt and pepper and mix until well combined.
To assemble lasagna: Spread half of the marinara sauce in a 9-by-13-inch baking dish. Layer cooked lasagna noodles over marinara sauce. Dollop about half the ricotta mixture on top and use a spatula to spread it evenly over the noodles. Arrange one layer of eggplant on top; reserve half of it for the second layer. Top with mozzarella cheese and sprinkle some Parmesan cheese over the top as well. Repeat everything with a second layer: the marinara sauce, lasagna noodles, ricotta mixture, roasted eggplant, mozzarella cheese and Parmesan cheese.
Lower oven temperature to 375 degrees. Cover with lasagna with foil and bake covered for 25 minutes, remove foil and bake for another 20 to 25 minutes. During the last 5 minutes of baking time: raise temp to broil (500 or 550) and bake for the last 5 minutes to brown the top of the lasagna. Be sure to watch your lasagna so you don't burn it.
Let cool for about 10 minutes to allow the lasagna to set. Slice, serve and enjoy! To freeze any leftovers: slice into pieces* (or leave whole) and store in freezer safe plastic bags or any freezer safe container. To reheat, bake in a 350 degree oven for 20 to 25 minutes, or until heated through.
Notes
*if you are going to reheat the lasagna and eat in individual slices, it's easier to already have the slices cut.