Preheat your oven to 375°F (190°C).

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

Cook the lasagna noodles in salted water until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil and sauté onions until translucent, about 3-4 minutes. Add minced garlic and cook for another minute.

Add sliced mushrooms, thyme, salt, and pepper to the skillet. Cook until tender, about 5-7 minutes.

Stir in spinach and cook until wilted, about 2-3 minutes. Remove from heat and mix in ricotta cheese.

Spread marinara sauce on the bottom of the baking dish. Layer with noodles, half of the ricotta mixture, and a sprinkle of mozzarella and Parmesan.

Repeat layers with remaining ingredients, ending with sauce and cheese on top.

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

Let lasagna cool for about 10 minutes before slicing and serving.