Preheat oven to 350 degrees.

Put raw cashews and a cup of water into a high-speed blender. Blend until completely smooth. Then set aside.

Fill a pot with steamer insert with about an inch of water. Bring to a boil. Put trimmed and halved green beans into the steamer insert and cover with a lid. Steam until the green beans are bright and tender, about 5 minutes.

To keep their bright color and stop their cooking, pour the green beans into a colander in the sink, and run cold water over them. Turn them occasionally so that all of the green beans get cool. Once the green beans are cold, pour them onto a clean kitchen towel to dry while you continue with the rest of the recipe.

Bring a large non-stick skillet to a medium heat, and add avocado oil. Scatter the sliced mushrooms across the skillet, and top with salt. Saute about 10 minutes, until the mushrooms are tender and have released their liquid.

Add vegan butter and garlic. Allow the butter to melt and garlic to soften and become fragrant, about 30 seconds. Then top the mushrooms with red wine vinegar.

Sprinkle flour on top of the mushrooms, and use a spatula to combine and slightly cook the flour for about a minute.

Add 1 cup of water, Better Than Bouillon no chicken base, and pepper to the skillet. Use a spatula to combine, being careful to get everything off the bottom of the skillet, while the sauce reduces and thickens.

Once the sauce has the consistency of gravy, stir in tamari.

Pour the reserved cashew sauce from the blender into the skillet. Bring to a simmer, then lower heat and stir frequently, until the sauce is quite thick, roughly 5 minutes. Remove from the heat.

Stir in the green beans and ⅔ cup French fried onions.

Transfer the green bean casserole to an 8x8 baking dish, and top evenly with the remaining ⅔ cup of French fried onions.

Put the baking dish in the oven, and bake until the sauce is bubbly around the edges and the onions are nicely browned, about 10 minutes.