Cook spaghetti as directed on package. Drain.
Meanwhile, melt margarine in Dutch oven over medium heat. Add mushrooms; cook 5 minutes or until tender, stirring frequently. Reduce heat to medium-low. Add flour; cook and stir until bubbly. Gradually add broth, stirring constantly, until mixture boils and thickens. Remove from heat; stir in half-and-half, sherry, 1/4 cup parsley, salt, nutmeg and pepper.
Add cooked spaghetti and turkey to mushroom mixture; stir gently to mix. Spoon mixture into ungreased 13x9-inch (3-quart) glass baking dish. Cover with foil; refrigerate at least 8 hours or overnight.
Heat oven to 350°F. Uncover baking dish; sprinkle Parmesan cheese over top. Cover; bake at 350°F. for 45 to 55 minutes or until thoroughly heated, removing foil during last 10 minutes of baking time. Sprinkle with parsley.