Preheat oven to 375 degrees F. In two 12- to 14-oz. ramekins or individual au gratin dishes layer the turkey and green beans. Top with mashed potatoes, spreading to an even layer. Cover with foil. Bake for 30 minutes. Remove foil and sprinkle with cheese. Bake, uncovered, 5 minutes more or until cheese is melted. Sprinkle with chives, if desired.