Chop the mushrooms into small bite-sized pieces. Then put oil in the bottom of a saucepan and sauté the mushrooms in the oil over medium heat.
Sprinkle the salt over the mushrooms and cook mushrooms until they get darker and release their juices.
Add dairy-free milk, garlic powder, paprika, black pepper, and soy sauce (optional) and heat until the soup just barely begins to bubble then reduce the heat to low.
In a separate container, mix the cornstarch and water and stir until it dissolves completely.
Pour the cornstarch mixture into the hot soup stirring constantly until it starts to bubble and thicken, then turn off the heat.
Place green beans in the bottom of a casserole dish and pour the soup over the beans and mix well.
Sprinkle fried onions over top of the casserole.
Bake for 35- 45 minutes until it is bubbly and the onions are golden brown. (Bake time will vary depending on the size of the beans or if you used fresh or frozen).
Let it cool down for about 10 minutes before serving to set up and get more firm.
Notes
If you don't want your fried onions to be too brown, sprinkle them on after you bake the casserole for about 25 minutes.
If you need the casserole to cook faster, blanch the beans in boiling water for about 5 minutes and then drain before adding them to the casserole. This will cut the cooking time by about 15 minutes.
The petite french beans will also cook faster than the large green beans.
You will know when it's done when the casserole is bubbling and you can easily stick a for in your beans.
If you don't like fried onion or can't find them, you can sprinkle crushed up crackers of choice on top.
Note: This is a large recipe since it's usually made for large holiday dinners. If you are making this for a side dish for a small family, you will want to cut the recipe in half.