Preheat the oven to 350°F
Grease a 1 1/2-quart baking dish
Drain 2 cans green beans or prepare 4 cups cooked green beans
Mix 1 can cream of mushroom soup with 1/2 cup milk in a bowl
Stir in 1/4 teaspoon black pepper
Add the green beans and 1 1/3 cups crispy fried onions
Transfer the mixture to the baking dish
Bake for 25 minutes
Stir the casserole
Top with 1/2 cup crispy fried onions
Bake for 5 more minutes until the onions are golden and the casserole is hot
Let it rest for a few minutes before serving