Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add 1 chopped onion and cook until translucent, about 5 minutes. Stir in 3 minced garlic cloves and sauté for an additional minute until fragrant, making sure not to let them brown.

Add 8 ounces of sliced mushrooms and cook for 8–10 minutes until browned and the moisture has evaporated. Season with 1 teaspoon of dried thyme, 1 teaspoon of oregano, salt, and pepper to taste. Pour in ½ cup of white wine and let it bubble until the wine has evaporated, then stir in 1 cup of grape tomatoes for 2–3 minutes until softened. Set the mixture aside.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Whisk in ¼ cup of all-purpose flour and cook for 2–3 minutes until golden, stirring continuously. Gradually add 2 cups of warmed milk, whisking constantly until the mixture thickens, about 5–7 minutes. Season with a pinch of nutmeg, salt, and pepper.

Preheat your oven to 375°F (190°C). Boil the lasagna noodles according to the package instructions until al dente, usually around 8 minutes. Drain the noodles and lay them flat on parchment paper to prevent sticking while you prepare the lasagna layers.

In a baking dish, spread a thin layer of Bechamel sauce. Place a layer of noodles on top, followed by half the mushroom mixture, 1 cup of chopped spinach, one-third of the Bechamel sauce, and one-third of the mozzarella cheese. Repeat these layers, finishing with a final layer of noodles topped with the remaining sauce and cheese.

Cover the dish tightly with aluminum foil and bake the mushroom lasagna in the preheated oven for 25 minutes. Remove the foil and bake for an additional 20 minutes, or until the top is golden and bubbling.

Once baked, let the lasagna rest for 10 minutes before serving. Garnish with fresh basil leaves if desired.