Lightened Up Green Bean Casserole

2 cups of frozen green beans

1 can pieces and stems mushrooms

¾ cup chicken broth

1 tbls corn starch

1 tsp ground mustard

1 cup French  onion rings

1 tbls butter.

In a small casserole dish combine all ingredients except onion rings.  Stir, bake at 375 for 25 minutes.  Sprinkle French onions on top and continue to bake until brown about 5 more minutes.