Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C).
Mix green beans, condensed cream of mushroom soup, milk, and ½ of the fried onions in a medium casserole dish.
Bake in the preheated oven until heated through and bubbly, about 25 minutes.
Sprinkle remaining onions on top, and return to the oven for 5 minutes. Season with salt and pepper to taste. Serve hot.
