Preheat your oven to 375°F (190°C). Cook the lasagna noodles according to package instructions until al dente. Drain and set aside on a clean kitchen towel to prevent sticking.
In a large skillet, heat the olive oil over medium heat. Add the chopped onion and cook until translucent, about 3-4 minutes.
Stir in the minced garlic and sliced mushrooms, cooking until the mushrooms are softened and liquid is released, approximately 5-7 minutes.
Add the fresh spinach, oregano, salt, and black pepper, cooking until the spinach wilts, about 2-3 minutes. Remove from heat and let cool for a few minutes.
In a mixing bowl, combine the cooked mushroom-spinach mixture with ricotta cheese, half of the mozzarella (1/2 cup), and half of the Parmesan cheese (1/4 cup). Mix well to combine.
Spread a thin layer of marinara sauce on the bottom of a 9x13 inch baking dish.
Take one lasagna noodle, place about 2-3 tablespoons of the filling at one end, and roll it up tightly. Place it seam-side down in the baking dish. Repeat with remaining noodles and filling.
Once all rolls are assembled in the dish, pour the remaining marinara sauce over the rolls, ensuring they are well covered. Sprinkle the remaining mozzarella and Parmesan cheese on top.
Cover with foil and bake in the preheated oven for 25 minutes. Then, remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Let the lasagna rolls cool for about 5 minutes before serving.
Notes
Serve the rolls garnished with fresh basil or parsley, and a sprinkle of extra grated Parmesan for a beautiful finish. A side of mixed greens would complement this dish nicely!