Preheat the oven to 350 degrees F. Stir the soup, soy sauce, black pepper, beans, and ⅔ cup of the onions in a 1½-quart casserole.
Bake until the bean mixture is hot and bubbling, 25 minutes. Stir the bean mixture. Sprinkle with the remaining onions.
Bake until the onions are golden brown, 5 minutes.