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

Add sliced mushrooms to the skillet. Sauté for 8-10 minutes until browned. Season with salt, pepper, thyme, and oregano. Optionally add white wine and simmer for 2-3 minutes.

Stir in halved grape tomatoes and cook for 2-3 minutes until softened. Remove from heat and set aside.

In a saucepan, melt butter over medium heat. Whisk in flour until golden, then gradually add warmed milk, whisking until thickened, about 5-7 minutes. Season with nutmeg, salt, and pepper.

Preheat oven to 375°F (190°C) and cook lasagna noodles according to package instructions. Strain and set aside.

In a baking dish, spread a layer of Bechamel sauce, followed by a layer of noodles, half the mushroom mixture, spinach, mozzarella, and Parmesan. Repeat layers, finishing with noodles and Bechamel on top.

Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for another 20 minutes until the top is golden and bubbling.

Let the lasagna rest for 10 minutes before slicing. Garnish with fresh basil if desired.