Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add chopped onions and sauté until translucent, about 5 minutes. Stir in minced garlic and cook for an additional minute.

Incorporate sliced mushrooms into the skillet, stirring occasionally. Cook until browned and moisture has evaporated, about 8 to 10 minutes.

Sprinkle in dried thyme, oregano, salt, and pepper. If using white wine, pour it in and cook down for 2 to 3 minutes.

Stir in halved grape tomatoes and cook until softened, about 2 to 3 minutes. Set aside.

In a saucepan, melt 4 tablespoons of butter. Whisk in 4 tablespoons of flour, cooking until lightly golden, about 2 to 3 minutes.

Gradually pour in 3 cups of warmed milk while whisking. Continue whisking until thickened, about 5 to 7 minutes. Season with nutmeg, salt, and pepper.

Preheat your oven to 375°F (190°C). Prepare the lasagna noodles according to package instructions.

Spread a thin layer of Bechamel sauce in a 9x13 inch baking dish. Layer noodles, half of the mushroom-tomato mixture, half of the spinach, and a third of the Bechamel sauce topped with a third of the mozzarella and Parmesan.

Continue layering with another set of noodles, the remaining mushroom-tomato mixture, the rest of the spinach, and additional Bechamel, finishing with the remaining cheese.

Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for an additional 20 minutes until golden and bubbly.

Let the lasagna rest for 10 minutes before serving. Optionally garnish with fresh basil.