Preheat your oven to 350°F (175°C). In a 1 1/2-quart baking dish, combine the condensed cream of mushroom soup, milk, and black pepper. Stir well until the mixture is smooth and thoroughly blended.

Add the drained green beans to the dish along with 2/3 cup of the French-fried onions. Mix everything gently to ensure the beans are evenly coated with the soup mixture.

Place the dish in the preheated oven and bake for 30 minutes or until the casserole is hot and bubbling. Remove the dish from the oven and stir to blend the flavors.

Sprinkle the remaining 2/3 cup of French-fried onions evenly over the top of the casserole. Return the dish to the oven and bake for an additional 5 minutes, or until the onions on top are crisp and golden. Serve warm.