Preheat your oven to 350°F and lightly grease a 9x13-inch baking dish.
In a large mixing bowl, combine the cream of mushroom soup, sour cream, garlic powder, black pepper, and salt until smooth.
Add the drained green beans, 3/4 cup of the fried onions, and the shredded cheddar cheese to the soup mixture, stirring until everything is well coated.
Pour the mixture into the prepared baking dish and spread evenly.
Bake uncovered for 25 minutes, then remove from oven and top with the remaining 3/4 cup fried onions.
Return to the oven and bake for an additional 10 minutes until the onions are golden brown and the casserole is bubbly.
Let stand for 5 minutes before serving to allow the sauce to thicken slightly.