Preheat oven to 450°.
Combine broth and next 4 ingredients in a bowl, stirring well.
Melt butter in a large nonstick skillet coated with cooking spray over medium-high heat. Add mushrooms and celery; sauté 5 minutes. Add broth mixture and sherry; cook 2 minutes or until thick, stirring constantly. Add cooked spaghetti and turkey. Cook until thoroughly heated. Spoon into an 11 x 7-inch baking dish coated with cooking spray. Top with cheese.
Bake at 450° for 10 minutes or until cheese melts.