Preheat oven to 400°F (200°C).
Place diced potatoes and sliced smoked sausage on a large baking sheet.
Drizzle olive oil over the mixture and sprinkle ranch seasoning garlic powder and black pepper.
Toss everything together until evenly coated.
Spread evenly on the baking sheet in a single layer.
Bake for 25–30 minutes stirring halfway through until potatoes are tender and lightly crispy.
Remove from oven and sprinkle cheddar and Parmesan cheese over the top.
Return to oven for 5 minutes until cheese is melted.
Garnish with chopped parsley and serve warm.