Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish.
In a large mixing bowl, combine cream of chicken soup, sour cream, 1 ½ cups cheddar cheese, green onions, garlic powder, black pepper, and paprika. Mix until smooth.
Stir in the hash brown potatoes until evenly coated.
Fold in the sliced kielbasa sausage.
Spread the mixture into the prepared baking dish.
Sprinkle the top with the remaining ½ cup of cheddar cheese.
For a crunchy topping, mix melted butter with crushed cornflakes or crackers and scatter over the casserole.
Bake uncovered for 40–45 minutes, until the casserole is bubbly and the topping is golden brown.
Let rest for 5 minutes before serving.
