Flounder Au Gratin
["1 Tbsp. margarine", "4 green onions, cut into 1/2-inch pieces", "2 Tbsp. diced celery", "2 tsp. all-purpose flour", "1/2 tsp. salt", "1/8 tsp. white pepper", "1/2 c. skimmed milk", "1/4 c. shredded Swiss cheese", "1 (16 oz.) pkg. frozen flounder fillets, thawed and drained", "1 Tbsp. fresh parsley, minced"]
["Melt margarine in small saucepan over low heat.", "Add onions and celery; saute until tender.", "Stir in flour, salt and pepper; cook 1 minute, stirring constantly.", "Gradually add milk; stir well.", "Cook over medium heat until thick and bubbly, stirring constantly.", "Add shredded Swiss cheese; reduce heat and cook until cheese melts, continuing to stir.", "Set aside.", "Arrange fillets in single layer in a 10 x 6 x 2-inch baking dish coated with vegetable cooking spray. Pour cheese mixture evenly over fillets.", "Cover; bake at 350\u00b0 for 25 minutes, or until fish flake easily.", "Sprinkle with parsley. Yields 4 servings."]
["margarine", "green onions", "celery", "all-purpose flour", "salt", "white pepper", "milk", "Swiss cheese", "frozen flounder", "fresh parsley"]