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

Add 8 cups of sliced mushrooms to the skillet and sauté for 8-10 minutes until they are browned and tender. Season with salt, pepper, 1 teaspoon of dried thyme, and 1 teaspoon of oregano. If using white wine, pour in a splash now and cook until the liquid evaporates (2-3 minutes). Stir in 2 cups of halved grape tomatoes and cook for another 2-3 minutes until they soften.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Whisk in 1/4 cup of flour and let it cook for about 2-3 minutes until golden, creating a roux. Gradually pour in 3 cups of warmed milk while whisking continuously until the sauce thickens (5-7 minutes). Season your Bechamel with a pinch of nutmeg, salt, and pepper.

Preheat your oven to 375°F (190°C). Cook and drain 12 lasagna noodles according to package instructions. Spread a layer of Bechamel sauce on the bottom of a 9x13-inch baking dish. Layer noodles, half of the mushroom mixture, half of the fresh spinach, followed by a drizzle of Bechamel and a mixture of shredded mozzarella and parmesan cheeses. Repeat layers until ingredients are exhausted, finishing with a layer of noodles topped with remaining Bechamel and cheeses.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. After that, remove the foil and bake for an additional 20 minutes until the top is golden and bubbly.

Once baked, remove the Mushroom Lasagna from the oven and let it rest for 10 minutes. Garnish with fresh basil before serving.