Preheat your oven to 350°F and grease a 1-1/2-quart baking dish with a tablespoon of butter.
Cook the spaghetti just shy of al dente in a large pot of salted water, then drain it well.
Melt butter in a skillet over medium heat, add mushrooms, and cook for 3-4 minutes until softened.
Stir the flour into the mushrooms, cook for 2 minutes, then gradually whisk in chicken broth until smooth.
Add heavy cream, turkey, and half of the Parmesan to the mushroom mixture. Season with salt and pepper.
Combine the cooked spaghetti with the creamy turkey mixture, then pour it all into the greased baking dish.
Top with the remaining Parmesan and bake for about 25 minutes, or until golden and bubbly.
Garnish with fresh parsley before serving.