Combine the milk and lemon juice in a bowl (this makes a vegan buttermilk). Add the onions and let them sit for 20-30 minutes (or in fridge overnight).
In a large zip lock, combine the flour, salt and garlic powder. Close bag and shake well.
Remove the onions from the milk and drain off excess liquid. Place the onions in the bag and gently shake around until all onions are coated.
Place oil in a large pan over medium heat until hot. You can test if it's ready by placing the edge of a prepared onion in the oil. If it sizzles, you are ready to start frying
Fill the pan with the onions, but don't overcrowd them, because this will cause steam between them (you'll likely need to fry them in a few batches). Fry evenly on both sides, until light golden brown (about 1-2 minutes each side). Add more oil as needed. These cook quickly so keep a close eye so they don't burn. When done, place on a large paper towel-lined plate to absorb excess oil.
Preheat oven to 350 °F (177 °C)
In a large pot, bring salted water to a boil and add green beans. Cook for 5 minutes. Remove from heat and rinse with cool water to stop them from cooking further. Drain well and set aside.
Blend the soy milk and cashews (discard soaking water) together until very smooth. Set aside.
In a large pan, heat butter over medium heat. Add onions and sauté until translucent, about 3-4 minutes.
Add mushrooms and sauté until their liquid releases and cooks down. Brown them a bit for about 5-6 minutes.
Add minced garlic, salt, pepper and spices. Cook 1 minute.
Turn heat up to med-high and add the white wine. Once it simmers, lower back to medium heat. Cook down liquid about 4-5 minutes.
Add flour to the pan and stir constantly for 30-60 seconds. Now slowly add the vegetable broth while constantly stirring. Stir in soy sauce. Let it simmer and thicken for 6-8 minutes.
Turn heat to low and add the soy milk and cashew mixture. Stir constantly to prevent burning. Cook for 1-2 minutes. Taste for seasoning and add as needed.
Add green beans into the pan and fold to combine. Add green bean mixture into a lightly greased casserole dish. Cover with fried onions and place in the oven. Bake uncovered for 20-30 minutes until heated throughout. Enjoy!
* Prep time doesn't include soaking time for onions or cashews.*I like to have extra onions for the table, so I use two large onions. I double the recipe above. They are a big hit every year.