Preheat the oven to 450 degrees F.
Cut each of the zucchini in half crosswise and then slice lengthwise into 1/4-inch strips. Toss with 1 tablespoon of the oil and a pinch of salt, and spread on a baking sheet. Cut the portabellas into 1/4-inch strips, and then toss in the remaining 1 tablespoon oil and a pinch of salt and place on a separate baking sheet. Roast for 7 to 8 minutes, then flip and roast until tender and starting to brown, 4 to 5 minutes. The portabellas may take a few minutes longer than the zucchini. Cool the vegetables. Reduce the oven temperature to 350 degrees F.
While the vegetables roast, mix 1/2 cup of the Parmesan, the pepper, nutmeg, ricotta, eggs, basil and 1 teaspoon salt in a large bowl until well combined.
Spread 1 1/2 cups of the marinara in the bottom of a baking dish and top with an even layer of uncooked lasagna noodles (about 5). Top the noodles with 1 1/2 cups of the ricotta mixture, spreading as evenly as possible. Evenly distribute half of the roasted veggies over the ricotta and top with 2 cups of the spinach. Add another 1 1/2 cups of marinara and another layer of noodles. Repeat with another 1 1/2 cups ricotta, the other half of the roasted vegetables, half of the mozzarella slices, the remaining 2 cups spinach, 1 1/2 cups of marinara, and then another layer of noodles. For the final layer, spread the remaining 1 1/2 cups ricotta, another layer of noodles, 1 1/2 cups of marinara, the remaining mozzarella slices, and then top with the remaining 1/2 cup of Parmesan.
Bake for 1 hour covered with foil. Then remove the foil and bake until bubbly and beginning to brown, 20 to 25 minutes. Rest the lasagna 15 to 20 minutes before serving.
Recipe courtesy of Amanda Freitag