Place green beans in a 1 1/2-quart, heat-resistant, non- metallic casserole. Top with slices of meat.
In a small bowl, combine soup, mayonnaise and mustard. Blend together well.
Pour soup mixture over meat slices.
Top with cheese.
In a small, heat-resistant, non-metallic bowl, melt 1 tablespoon of butter in Microwave Oven 15 seconds.
Toss croutons in melted butter.
Sprink1e buttered croutons over cheese.
Heat, uncovered, in Microwave Oven 10 minutes. Let stand for 5 minutes before serving.