Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the fresh green beans, Campbell's cream of mushroom soup, milk, salt, and pepper.
Transfer the mixture into a 2-quart baking dish and spread it out evenly.
Bake in the preheated oven for 25 minutes, or until the beans are tender and the mixture is bubbly.
Remove from the oven and sprinkle crispy fried onions on top.
Return the dish to the oven and bake for an additional 10-15 minutes, until the onions are golden brown.
Let the casserole cool for a few minutes before serving.