1. Pour the cream of mushroom soup over the blanched green beans. Stir gently to coat the beans in the cream sauce. Add parmesan cheese (optional).
2. Transfer to baking dish and spread in an even layer.
3. Top with mushrooms and additional parmesan cheese.
4. Melt butter, and mix with GF panko. Sprinkle on top, with extra parmesan, and bake until golden, and bubbly.
5. Remove from the oven and top with the crushed crispy fried onions. Press the onions down gently and serve.