Oil a medium sized pot and start sautéing your onions, mushrooms, and stock cube in a few table spoons of almond milk
When your onions and mushrooms have softened, add the remaining almond milk and bring to a simmer
Next, in a separate bowl or cup, mix corn starch with a bit of cold water (enough to dissolve it) and add to the almond milk mixture. Let boil for one minute. Repeat this step to recieve desired thickness
Once your sauce has thickened, add your salt, pepper, garlic powder, nutritional yeast, and whatever else you want
Finally, mix in your green beans and empty your mixture into a casserole dish. Cover the top with those yummy crispy onions and bake at 350F for 20 minutes.