Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with olive oil.

Cook the lasagna noodles in salted boiling water until al dente, about 8–10 minutes. Drain and rinse.

Sauté diced onion in olive oil until translucent, then add minced garlic and cook for an additional minute.

Add sliced mushrooms, dried thyme, salt, and pepper. Cook until mushrooms are tender, then fold in chopped spinach.

Assemble layers: pour marinara sauce, add noodles, ricotta, mushroom-spinach mixture, mozzarella, and Parmesan. Repeat the layers.

Cover with foil and bake for 25 minutes, then remove foil and bake for an additional 10–15 minutes until golden.

Let the lasagna cool for 10 minutes before slicing and serve warm, garnished with fresh basil.