Preheat the Oven: Preheat your oven to 375°F (190°C).

Cook the Spaghetti: Cook the spaghetti according to package directions until just al dente. Drain and set aside.

Prepare the Mushroom Mixture:

In a large skillet, melt the butter over medium heat.

Add the sliced mushrooms and chopped onion. Cook until the mushrooms are tender and the onions are translucent, about 5-7 minutes.

Stir in the lemon juice and cook for another minute.

Make the Sauce:

Sprinkle the flour, salt, paprika, and nutmeg over the mushroom mixture. Stir to combine and cook for 1-2 minutes to get rid of the raw flour taste.

Gradually whisk in the chicken broth and half and half. Cook, stirring constantly, until the mixture thickens and bubbles.

Combine with Turkey and Pasta:

Add the cooked turkey and cooked spaghetti to the sauce. Stir everything together until well combined.

Add Parmesan:

Stir in the grated Parmesan cheese until melted and well incorporated into the sauce.

Transfer to Baking Dish:

Grease a 9x13 inch baking dish. Transfer the turkey mixture to the prepared baking dish and spread it out evenly.

Bake:

Sprinkle the top with a little more paprika for color.

Bake in the preheated oven for 25-30 minutes, or until the top is golden and the sauce is bubbly.

Serve:

Let it cool for a few minutes before serving. This dish goes well with a side of green salad or some crusty bread.

Enjoy your delicious Turkey Tetrazzini!