Prepare the filling: In a large bowl, combine the ricotta cheese, spinach, mushrooms, tomato puree, mozzarella cheese, oregano, salt, and pepper. Mix well.
Assemble the lasagna: Preheat oven to 180°C (356°F). Grease a baking dish. Layer the bottom with hearts of palm lasagna sheets. Spread a layer of the cheese and vegetable mixture over the lasagna sheets. Repeat layers until all ingredients are used, ending with a layer of lasagna sheets.
Bake: Sprinkle with Parmesan cheese. Bake for 30-40 minutes, or until the lasagna is bubbly and the cheese is golden brown.
Serve: Let cool for a few minutes before serving. Garnish with fresh basil.