Step 1: Prepare the Vegetables

Sauté the Mushrooms:

• Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the sliced mushrooms, season with salt and pepper, and cook until golden brown, about 5–7 minutes. Set aside.

Cook the Spinach:

• In the same skillet, add the remaining tablespoon of olive oil and sauté the chopped spinach for 3–4 minutes, until wilted. Season lightly and set aside.

Step 2: Make the Béchamel Sauce

Create the Roux:

• Melt butter in a medium saucepan over medium heat. Stir in the flour and whisk constantly for 1–2 minutes until a light golden paste forms.

Add Milk Gradually:

• Slowly pour in the milk, whisking continuously to avoid lumps. Simmer gently until the sauce thickens, about 5–7 minutes.

Season the Sauce:

• Add garlic powder, onion powder, nutmeg (if using), salt, and pepper. Stir well and set aside.

Step 3: Prepare the Ricotta Mixture

• In a mixing bowl, combine the ricotta cheese, egg, and half of the grated Parmesan. Season with salt and pepper. Mix until smooth.

Step 4: Assemble the Lasagna

Preheat the Oven:

• Set your oven to 375°F (190°C).

Layer the Lasagna:

• Grease a 9×13-inch baking dish. Spread a thin layer of béchamel sauce on the bottom. Layer as follows:
• Lasagna noodles
• Half of the ricotta mixture
• Sautéed spinach
• Mushrooms
• Béchamel sauce
• Mozzarella cheese
• Repeat the layers, finishing with noodles, béchamel, mozzarella, and the remaining Parmesan.

Step 5: Bake

Cover and Bake:

• Cover the dish with foil (spray the foil with oil to prevent sticking). Bake for 30 minutes.

Uncover and Finish:

• Remove the foil and bake an additional 15–20 minutes, or until the top is golden and bubbly.

Let it Rest:

• Allow the lasagna to cool for 10–15 minutes before slicing to help the layers set.