Preheat your oven to 375°F (190°C).

Grease a 9×13-inch baking dish with olive oil or cooking spray.

Cook lasagna noodles in salted water until al dente, about 8 to 10 minutes, then drain and cool.

In a skillet, heat olive oil over medium heat, sauté chopped onion for 3-4 minutes, add minced garlic and cook for another minute.

Add sliced mushrooms to skillet, season with thyme, salt, and pepper, and cook for 5-7 minutes until tender.

Stir in chopped spinach; cook until wilted for 2-3 minutes, then remove from heat.

Assemble lasagna by spreading marinara sauce on the bottom of the dish, layer three noodles, half ricotta, half mushroom-spinach mix, and sprinkle with mozzarella and Parmesan.

Repeat layering with remaining ingredients and top with marinara sauce.

Cover with foil and bake for 25 minutes, then uncover and bake for another 10-15 minutes until cheese is bubbly and golden.

Let cool for 10 minutes, garnish with fresh basil if desired, slice and serve warm.