Preheat your oven to 375°F and grease a 9x13-inch baking dish.
Cook the Pasta
Boil the spaghetti or egg noodles until al dente, then drain and set aside.
Sauté Vegetables
Heat olive oil in a skillet over medium heat. Add the onions and garlic, cooking until fragrant. Toss in mushrooms and cook until softened.
Make the Sauce
Add butter to the skillet. Once melted, sprinkle in the flour and whisk continuously for 1-2 minutes to create a roux. Slowly pour in the broth, milk, and heavy cream while whisking to prevent lumps.
Season & Thicken
Stir in salt, pepper, paprika, and nutmeg. Let simmer for 3-4 minutes until thickened.
Combine Ingredients
Mix in the turkey, frozen peas, sour cream, Parmesan cheese, and cooked noodles. Stir well.
Assemble & Bake
Transfer the mixture to the baking dish. Sprinkle mozzarella cheese evenly over the top. In a small bowl, combine breadcrumbs with a tablespoon of melted butter, then sprinkle over the cheese.
Bake & Serve
Bake uncovered for 25-30 minutes or until golden and bubbling. Let cool slightly before serving.