Bring a large pot of water to boil and add the salt. Add green beans and cook for 5 minutes. Drain and set aside.
In a large skillet over medium heat, add vegan butter and shallots and garlic. Season with salt and pepper and stir.
Cook for 3 minutes, then add mushrooms and season with a bit more salt and pepper. Cook for 4-5 minutes or until lightly browned.
Add flour and stir. Cook for 1 minute, then slowly add in vegetable broth, whisking to incorporate.
Add non-dairy milk and whisk to stir again. Season with a touch more salt and pepper bring to a simmer, then reduce heat to low to thicken. Cook for 7-8 minutes, or until mixture thickens. Taste and adjust seasonings as needed.
Remove from heat and add 1/2 cup of the fried onions and all of the cooked green beans. Stir and top with remaining fried onions.
Bake for 15 minutes, or until warmed through and lightly browned.