There are a few GF canned mushroom soups out there, some of them cause me to react digestively to the preservatives in them but the Walnut Acres soup didn't give me any problems. The only place I've seen this is Oak Street Natural Market, I haven't really looked for it anywhere else. It's not as thick as some of the other GF cream of mushroom soups so try the different brands and see which one you like best. I know Healthy Valley makes a GF soup and you can find it at most grocery stores.
Turkey Potato Casserole
Adapted from All Recipes
2 C cooked turkey, shredded
1 onion, chopped
2 cans green beans, drained
1 can GF cream of mushroom soup
16 oz cheddar cheese, shredded - use Daiya for a DF option
4 C prepared mashed potatoes
Preheat oven to 350 F.
In a 9x13 baking dish layer the turkey evenly on the bottom. Top with the onion and green beans. Pour the soup over the beans and sprinkle 4 oz cheese on top. Mix together the mashed potatoes and 8 oz of cheese then spread over the casserole and seal the edges.
Bake for 40 minutes or until heated through. Top with the remaining 4 oz of cheese and bake until it's melted.