In a large saucepan, combine the green beans, salt and ¾ cup water. Bring to a boil, reduce heat, cover and simmer just until tender, about 8 minutes. Drain.
In a large skillet, melt 2 tablespoons butter over medium heat. Add the scallions and briefly sauté, until fragrant and tender, about 2 minutes. Add the 1 cup water and FODY Soup Base. Bring to a simmer. In a small bowl, whisk the milk and flour together until there are no lumps. Slowly add the milk mixture to the broth and scallions in the skillet, while constantly stirring. Continue to cook and stir until mixture is evenly thickened. Remove from heat. Stir in the mushrooms, pepper and the cooked green beans and then transfer to a 1 1/2 qt casserole dish.
Melt the remaining 1 tablespoon butter and combine with the breadcrumbs and almonds. Sprinkle evenly over the top of the casserole.
Bake about until bubbly and lightly browned, about 30 minutes. Serve.
Notes
*You can also use 1 cup homemade Low-FODMAP Chicken Stock instead of the water and FODY Soup Base; add salt to taste.