Preheat the oven to 400°F (200°C). Lightly grease a large baking dish or sheet pan.
In a large bowl, combine diced potatoes with olive oil, ranch seasoning, garlic powder, onion powder, salt, and pepper. Toss well to coat.
Spread potatoes evenly in the baking dish. Roast for 25–30 minutes, stirring once, until tender and golden.
While the potatoes roast, brown the smoked sausage in a skillet over medium heat for about 5 minutes until lightly crisp.
Remove potatoes from the oven and add the cooked sausage to the dish.
Stir in sour cream and half of the shredded cheddar until coated and creamy.
Sprinkle the remaining cheese on top and bake for another 10–12 minutes, until melted and bubbly.
Garnish with green onions or parsley and serve warm.