1. In a large saucepan, saute onion in butter until tender. Stir in flour until blended. Gradually add milk; cook and stir for 2 minutes or until thickened. Stir in cheese until melted. Add tomatoes and salt, stirring constantly. Add shrimp and peas; cook until shrimp turn pink. Serve with chow mein noodles; sprinkle with paprika. Yield: 6 servings.