Combine broccoli, water, and salt in a 2QT casserole. Cover with a tight-fitting lid or plastic wrap. Microwave on high for 10-12 minutes or until tender. Use a chopper to chop broccoli. Mix cornstarch and milk until smooth. Stir into broccoli. Add cheese and margarine. Microwave uncovered on high for 10 to 12 minutes, stirring as needed until thickened. Makes 3 to 4 servings.