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

Cook lasagna noodles according to package instructions until al dente, about 8-10 minutes. Drain and rinse with cold water.

Heat olive oil in a large skillet over medium heat. Sauté chopped onion for 5 minutes until translucent. Add minced garlic and cook for 1 more minute.

Add sliced mushrooms, dried thyme, salt, and pepper to the skillet. Cook for 8-10 minutes until mushrooms are tender.

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

Spread half of the marinara sauce at the bottom of the baking dish, place three noodles on top.

Spread half of the ricotta cheese over noodles, top with half of the mushroom and spinach mixture, and one-third of the mozzarella and Parmesan cheese.

Repeat layering with remaining components. Top with remaining cheeses.

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

Let cool for a few minutes before slicing and serve warm, garnished with fresh basil if desired.