Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add 1 chopped onion and sauté until translucent, about 5 minutes. Stir in 2 minced garlic cloves and cook for another minute until fragrant.

Add 8 cups of sliced mushrooms to the skillet. Cook for 8-10 minutes, stirring occasionally, until they release moisture and begin to brown. Season with 1 teaspoon dried thyme, 1 teaspoon dried oregano, salt, and pepper.

Optionally pour in ½ cup of white wine and let it simmer for 2-3 minutes until evaporated. Then, stir in 1.5 cups of halved grape tomatoes and continue cooking for another 2-3 minutes.

In a separate saucepan, melt 4 tablespoons of butter over medium heat. Whisk in 4 tablespoons of flour and cook for 2-3 minutes. Gradually add 3 cups of warmed milk, whisking until the sauce thickens.

Preheat your oven to 375°F (190°C). In a large pot, bring salted water to a boil and cook 12 lasagna noodles until al dente, about 8-10 minutes. Drain and lay them flat.

In a 9x13 inch baking dish, spread a layer of Bechamel sauce on the bottom. Layer 3 cooked lasagna noodles, half of the mushroom-tomato mixture, some spinach, and another layer of Bechamel.

Top with a sprinkle of mozzarella and Parmesan, and repeat until all ingredients are used, finishing with a layer of noodles and Bechamel on top.

Cover with aluminum foil and bake for 25 minutes, then remove the foil and continue to bake for an additional 20 minutes.

Once baked, let the Mushroom Lasagna rest for 10 minutes before slicing. Garnish with basil leaves if desired.