1. Preheat the oven to 350°F and lightly coat a baking dish with cooking spray.

2. Cook the spaghetti according to the package directions until al dente. Drain and set aside.

3. Place a large skillet over medium-high heat and coat with cooking spray. Add the butter and let it melt.

4. Add the mushrooms, onion, and celery to the skillet. Cook for about 6–8 minutes, stirring often, until the vegetables are tender.

5. In a separate bowl, whisk together the flour and milk until completely smooth.

6. Pour the milk mixture into the skillet along with the chicken broth, salt, and black pepper. Stir well and bring the mixture to a gentle boil.

7. Reduce the heat and simmer for about 5 minutes, stirring occasionally, until the sauce thickens slightly.

8. Remove the skillet from the heat. Stir in the cream cheese until melted and smooth.

9. Add half of the Parmesan cheese, garlic powder, pimiento, cooked turkey, cooked spaghetti, and parsley. Stir until everything is evenly coated.

10. Transfer the mixture to the prepared baking dish and spread evenly. Sprinkle the remaining Parmesan cheese over the top.

11. Bake for 25–30 minutes, or until hot and bubbly. Serve warm.