In a small saucepan, melt margarine and saute mushrooms and onions for 4 minutes, stirring occasionally. Add flour, cook 1 minute, stirring constantly. Gradually add milk, sherry, seasoning, pepper and nutmeg; cook 5 minutes until thickened, stirring constantly. Into 1-quart casserole coated with non-stick cooking spray, place spaghetti, turkey, pimento and sauce. Toss well and sprinkle with cheese. Bake at 350 for 20-25 minutes until hot and bubbly.