Preheat oven to 400°F (200°C) and lightly grease a baking sheet or large oven-safe skillet.
In a large bowl, combine potatoes, olive oil, ranch seasoning mix, salt, and pepper. Toss until evenly coated.
Spread potatoes evenly on the baking sheet and bake for 20 minutes.
Remove from oven, stir in sliced smoked sausage, and return to bake for another 15-20 minutes, or until potatoes are tender and lightly crispy.
Sprinkle shredded cheddar and mozzarella cheese over the top. Bake for an additional 5 minutes, or until cheese is melted and bubbly.
Garnish with fresh parsley before serving, if desired.