Preheat your oven to 350°F (175°C) to ensure it's ready for baking.
In a medium mixing bowl, whisk together the condensed cream of mushroom soup, milk, soy sauce, and black pepper until the mixture is smooth and well-combined.
Stir the thawed green beans and 2/3 cup of the French fried onions into the soup mixture, folding gently until the beans are evenly coated.
Pour the green bean mixture into an ungreased 1 1/2-quart casserole dish and spread it into an even layer.
Bake for 30 minutes, or until the casserole is hot and bubbling around the edges.
Carefully remove the casserole from the oven and stir it. Then, sprinkle the remaining 2/3 cup of French fried onions evenly over the top.
Return the casserole to the oven and bake for 5 more minutes, or until the onions on top are golden brown and crispy.