Preheat your oven to 350°F (175°C). Prepare all ingredients in advance to streamline the process.
In a medium-sized casserole dish, combine the green beans, condensed cream of mushroom soup, milk, and half of the French-fried onions. Mix thoroughly to ensure even distribution of flavors.
Transfer the dish to the preheated oven and bake until the mixture is heated through and bubbling gently, approximately 25 minutes.
Remove the casserole from the oven and evenly sprinkle the remaining French-fried onions over the top. Return to the oven and bake for an additional 5 minutes, allowing the topping to turn golden and crisp.
Season the casserole with salt and freshly ground pepper according to your preference. Serve immediately while hot.
