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

In a large pot, bring salted water to a boil and cook lasagna noodles according to package instructions until al dente, about 8-10 minutes. Drain and lay flat on a towel.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add chopped onion and sauté for 3-4 minutes until translucent, then add minced garlic and sauté for an additional minute.

Add sliced mushrooms, dried thyme, salt, and pepper to the skillet. Cook for 5-7 minutes until tender, then add chopped spinach and cook for another 2-3 minutes until wilted.

Layer the lasagna by spreading marinara sauce at the bottom of the baking dish, followed by three noodles, half of the ricotta cheese, half of the mushroom-spinach mixture, and a third of the mozzarella and Parmesan. Repeat layers finishing with marinara and remaining cheese.

Cover the assembled lasagna with foil and bake for 25 minutes, then remove foil and bake for an additional 10-15 minutes until cheese is bubbly and golden.

Allow the lasagna to cool for about 10 minutes before slicing and serving.