Preheat the oven to 350°F (175°C).
Bring a medium pot of salted water to a boil. Add the frozen green beans and cook for 2–3 minutes, just until tender-crisp.
Drain the green beans thoroughly and transfer them to a large mixing bowl.
Add the condensed cream of mushroom soup, milk, soy sauce, black pepper, seasoned salt, and 1 cup of the crispy fried onions. Stir gently until the beans are evenly coated.
Transfer the mixture to a 2-quart baking dish and spread it into an even layer.
Bake the Green Bean Casserole uncovered for 30–35 minutes, or until the sauce is hot and bubbling around the edges.
Remove the casserole from the oven and gently stir. Sprinkle the remaining ½ cup of crispy fried onions evenly over the top.
Return it to the oven and bake for another 10 minutes, or until the topping is crisp and golden brown.
Let the casserole rest for about 5 minutes before serving.