Preheat oven to 350°F. Cook noodles according to package directions, omitting salt. Drain; set aside.

Melt margarine in large nonstick skillet over medium-high heat. Add mushrooms and onions; cook and stir until onions are tender. Add chicken broth, 1/2 cup milk and sherry to onion mixture. Pour remaining 1/2 cup milk into small jar with tight-fitting lid; add flour, salt, nutmeg and pepper. Shake well. Slowly stir flour mixture into skillet. Bring to a boil; cook 1 minute. Reduce heat; stir in pimiento and 2 tablespoons Parmesan cheese. Stir in sour cream; blend well. Add chicken and noodles; mix well.

Lightly coat 1-1/2-quart casserole with nonstick cooking spray. Spread mixture evenly into prepared casserole. Sprinkle with remaining 2 tablespoons Parmesan cheese. Bake 30 to 35 minutes or until hot. Let cool slightly. Cut into 6 wedges before serving.