Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine diced potatoes, sour cream, shredded cheddar cheese, milk, diced onion, minced garlic, salt, pepper, and paprika. Mix until well combined.
Add the sliced kielbasa sausage to the potato mixture, gently folding it in to distribute evenly.
Pour the entire mixture into a greased 9x13 inch baking dish, spreading it out evenly.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes, or until the potatoes are tender and the top is golden and bubbly.
Once done, remove from the oven and let it cool for a few minutes before garnishing with chopped green onions.