In Dutch oven or large saucepan, cook spaghetti to desired doneness as directed on package. Drain; return to Dutch oven.
Meanwhile, melt margarine in medium nonstick saucepan over medium heat. Add garlic; cook 1 minute. Add mushrooms; cook 1 minute.
In small bowl, combine milk and flour; blend well.* Add to mushrooms in saucepan; cook, stirring constantly, until bubbly and thickened. Add spreadable cheese and 2 tablespoons of the Parmesan cheese; cook and stir until cheeses are melted. Stir in turkey.
Add sauce to cooked spaghetti; toss over low heat until well mixed. Sprinkle with remaining 2 tablespoons Parmesan cheese.