Preheat your smoker to 250°F (121°C) and grease an 8x8-inch baking dish thoroughly.

In a large mixing bowl, blend together one can of cream of mushroom soup, ½ cup of sour cream, and ¼ cup of milk. Add 1 teaspoon of salt and ½ teaspoon of garlic powder, mixing until smooth.

Gently fold in 18 ounces of thawed frozen green beans and ½ cup of French fried onions, ensuring each green bean is evenly coated.

Pour the green bean mixture into the greased baking dish and top with the remaining ½ cup of French fried onions.

Place the dish in the smoker and cook for about 1 hour or until hot and bubbly.

Check for doneness by inserting a fork to test if the green beans are tender and the casserole is heated through.

Remove the casserole from the smoker and let it cool for a few minutes before serving.