Preheat your oven to 375°F (190°C).

Grease a 9x13-inch baking dish with olive oil or cooking spray.

In a large pot, bring salted water to a boil. Cook the lasagna noodles until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Sauté chopped onion until translucent, about 3-4 minutes. Stir in minced garlic and cook for another 30 seconds.

Add sliced mushrooms, dried thyme, salt, and pepper. Sauté for about 5-7 minutes until tender.

Stir in chopped spinach and cook until just wilted, about 2-3 minutes.

Spread marinara sauce on the bottom of the baking dish, layer with three lasagna noodles.

Spoon half of the ricotta cheese over the noodles, followed by half of the mushroom and spinach mixture. Sprinkle with mozzarella and Parmesan.

Repeat layering with another three noodles, the rest of the ricotta, the remaining mushroom mixture, and more mozzarella and Parmesan.

Top the final layer with the remaining marinara sauce and sprinkle with additional mozzarella and Parmesan cheese.

Cover the dish with aluminum foil and bake for 25 minutes. Remove foil and continue baking for 10-15 minutes until bubbly and golden brown.

Allow the lasagna to cool for about 10-15 minutes. Garnish with fresh basil before serving.