Preheat your oven to 375°F (190°C).

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

Boil salted water in a large pot. Cook lasagna noodles until al dente, 8-10 minutes. Drain and set aside.

In a skillet, heat olive oil and sauté chopped onion until translucent. Add minced garlic, sliced mushrooms, thyme, salt, and pepper. Cook until mushrooms are tender. Stir in spinach until wilted.

Spread a layer of marinara sauce in the baking dish. Layer a third of noodles, half of ricotta, mushroom-spinach mix, and sprinkle mozzarella and Parmesan. Repeat, finishing with marinara and cheese on top.

Cover with foil and bake for 25 minutes. Remove foil and bake for another 10-15 minutes until golden brown.

Let rest for 10-15 minutes before slicing and serving.