Preheat oven to 350 degree Fahrenheit.
In a skillet, heat 1 tablespoon of oil on medium-high heat for 15-20 seconds. Add mushrooms, onions, salt, thyme, and saute for 4-5 minutes. Stir occasionally, but not constantly, to allow for golden crust to form on mushrooms. Add 1 clove crushed garlic during last 30 seconds of cooking.
Remove skillet from heat and set aside.
In a high-speed blender, place rinsed raw cashews, water, soy sauce, cornstarch, onion powder, and salt. Blend on high until mixture is completely smooth without any gritty cashew pieces.
Pour cashew mixture over sauteed mushroom and onion mixture in your skillet. Return skillet to medium heat, and stir constantly, until sauce has begun to bubble and thicken.
Place green beans (fresh blanched or semi-thawed frozen) in a cast iron skillet or 9 inch x 9 inch glass baking dish. Pour creamy thickened cashew and mushroom sauce over your green beans, and gently fold together.
Place in preheated oven and bake at 350 degrees for 20-25 minutes, or until casserole is hot and bubbling, and green beans are tender.
Sprinkle French fried onions over the top of casserole and bake for an additional 5 minutes until golden.
Serve warm and enjoy.