You won't miss the meat in this flavor-packed and hearty lasagna. It might take a while to prepare and assemble, but is definitely worth the effort!
Preheat the oven to 400 degrees. Cover the bottom of a large pot with about 1 inch water. Bring to a boil and add spinach. Cook for just a little while until it gets soft and shrinks; remove and drain well. In a large bowl, whisk together the ricotta cheese, eggs, salt, and pepper. Add the spinach (once it is completely cooled down) and stir to combine. In a separate bowl, combine the mozzarella and basil.
Heat a large skillet over medium heat and add the olive oil. Then, add the onions, mushrooms, carrots, and garlic, cook for about 2 minutes. Add the zucchini and eggplant, and cook until the vegetables are tender, 3 to 5 minutes. Remove from heat and season with salt and pepper.
Spread a third of the crushed tomatoes over the bottom of a 9-by-13-inch baking dish. Top with a layer of lasagna noodles. Spread over a layer of the ricotta mixture, followed by layer of teh vegetable mixture, and a layer of the mozarella. Repeat to make 2 more layers, ending with the shredded cheese on top. Bake for 30 minutes, covered with foil. Remove the foil and continue to bake until the top is golden brown, about 20 minutes more.
Let cool at least 15 minutes before serving.