Cook the Noodles: Boil a large pot of salted water. Add lasagna noodles and cook according to package instructions (about 8-10 minutes) until al dente. Drain and lay flat on a towel to prevent sticking.

Sauté Spinach and Mushrooms: Heat 2 tablespoons of olive oil in a skillet. Sauté sliced mushrooms for 5-7 minutes until golden brown. Add spinach and cook until wilted (2-3 minutes). Remove from heat.

Prepare Cheese Mixture: In a bowl, mix ricotta cheese with salt, pepper, and herbs until well blended.

Make Béchamel Sauce: Melt 4 tablespoons of butter in a saucepan. Whisk in flour for 2 minutes, then gradually add milk while whisking until thickened (5-7 minutes). Season with nutmeg.

Layer Lasagna: Preheat oven to 375°F (190°C). In a greased baking dish, layer béchamel sauce, noodles, cheese mixture, sautéed spinach and mushrooms. Repeat layers, finishing with béchamel on top.

Bake: Cover with foil and bake for 35 minutes. Remove foil, sprinkle with mozzarella and Parmesan, and bake uncovered for another 10-15 minutes until bubbly and golden.

Rest & Serve: Let the lasagna rest for 10-15 minutes before slicing and serving.