Preheat oven to 400°F. Grease a large rimmed baking sheet or spray with nonstick cooking spray. You can line the sheet pan with heavy-duty aluminum foil before greasing for easy cleanup, if desired.
In a large bowl, whisk together the dry Italian dressing mix, olive oil, garlic powder, and black pepper.
Add the potatoes and toss to coat.
Spread the potatoes (and any extra olive oil mixture) in a single layer on the prepared baking sheet.
Bake for 20 minutes, stirring the potatoes halfway through.
Add the sliced sausage to the pan. Stir the sausage and potatoes so that everything is nicely coated in the olive oil and seasoning.
Bake for 10 more minutes, or until the potatoes are crispy on the outside and tender on the inside, and the sausage is nicely browned.
Garnish with chopped fresh parsley, if desired. Serve immediately.