In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add 1 chopped onion and sauté until translucent, about 5 minutes. Stir in 2 minced garlic cloves, cooking for 1 additional minute. Then, add 8 ounces of sliced mushrooms, cooking until browned and tender, roughly 8-10 minutes. Season with salt, pepper, 1 teaspoon of dried thyme, and 1 teaspoon of dried oregano. If using, pour in ½ cup of white wine and let it evaporate for 2-3 minutes. Finally, stir in 1 cup of halved grape tomatoes, cooking until softened, about 2-3 minutes. Set aside.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Whisk in ¼ cup of all-purpose flour, stirring continuously until golden and bubbling, approximately 2-3 minutes. Gradually pour in 2 cups of warmed milk while whisking to avoid lumps. Continue to cook and stir until the mixture thickens to a creamy consistency, about 5-7 minutes. Season the sauce with a pinch of salt, pepper, and freshly grated nutmeg to taste, then set it aside.

Preheat your oven to 375°F (190°C). While the oven heats up, cook the lasagna noodles according to package instructions until al dente. Typically, this will take about 8-10 minutes. Drain the noodles and lay them flat on a clean kitchen towel to prevent sticking.

In a 9x13 inch baking dish, spread a thin layer of the prepared Bechamel sauce on the bottom. Begin layering with lasagna noodles, followed by half of the sautéed mushroom mixture, a layer of fresh spinach, and a drizzle of Bechamel sauce. Sprinkle with mozzarella and parmesan cheese. Repeat this layering process once more, finishing with a final layer of noodles and Bechamel sauce topped with cheese.

Cover the assembled Mushroom Lasagna with aluminum foil to prevent it from browning too quickly. Bake in the preheated oven for 25 minutes. After that, remove the foil and continue to bake for another 20 minutes or until the top is golden and bubbling. Let the lasagna rest for about 10 minutes before slicing to allow the layers to set.