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 1.5-quart 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. Let rest for a few minutes before serving.
