Divide olive oil, pepper, parmesan in half and set aside.
Chop spinach once thawed and chop basil
Preheat the oven to 400 degrees F.
Position racks in the upper and lower thirds of your oven. Lightly coat 2 rimmed baking sheets with nonstick spray. Coat a 9×13-inch baking dish with nonstick spray and set aside.
Arrange sliced eggplant in a single layer on the 2 sheet pans – if some of your end-most eggplant slices are very curved, trim off the eggplant outermost curvy portion so that the slices lay mostly flat. Brush 2 1/2 tablespoons of the oil over both sides of all of the slices. Sprinkle 1/2 teaspoon kosher salt and ¼ teaspoon pepper over the top.
Roast the eggplant until it is soft and golden, about 25 minutes, flipping the slices over and swapping the pans’ positions once halfway through. Remove the slices from the oven and reduce the oven temperature to 350 degrees F.
Meanwhile, in a large skillet heat the remaining 1/2 tablespoon oil over medium heat. Add the sliced mushrooms. Sauté until the mushrooms are soft, about 7 minutes. Add the minced garlic, next ½ teaspoon kosher salt, and oregano. Cook for another 2 minutes. Remove the pan from the heat. Add the marinara pasta sauce and stir to combine.
In a large bowl add the ricotta, 1/4 cup Parmesan, egg, and remaining 1/2 teaspoon salt and remaining 1/4 teaspoon pepper. Mix well, until the mixture is evenly combined. Stir in the spinach, using a fork to break it up and distribute it as evenly with the ricotta mixture as possible.
Spoon half of the mushroom marinara sauce on the bottom of the prepared baking dish and spread it into an even layer. Lay 4 eggplant slices on top followed by all of the ricotta mixture. Layer on another 4 slices of eggplant and finish with the remaining mushroom marinara sauce. Top with the mozzarella and remaining ¼ cup Parmesan. Bake for 25 to 30 minutes, until the cheese is melted and the lasagna is hot and bubbly. Remove from the oven and sprinkle with fresh herbs.