Preheat oven to 375°. Cook spaghetti according to package directions for al dente. Drain, reserving 2-1/2 cups pasta water; transfer spaghetti to a 13x9-in. baking dish coated with cooking spray. Dissolve bouillon in reserved pasta water., In a large nonstick skillet, heat butter over medium-high heat; saute mushrooms until tender. Stir in flour until blended. Gradually stir in sherry, reserved pasta water and seasonings. Bring to a boil; cook and stir until thickened, about 2 minutes. , Reduce heat to low; stir in milk and 1/3 cup cheese until blended. Add turkey; heat through, stirring constantly. Pour over spaghetti; toss to combine. Sprinkle with remaining cheese and, if desired, paprika., Bake, covered, until bubbly, 25-30 minutes.