Preheat the oven: Preheat your oven to 425°F (220°C). Line a large rimmed baking sheet with parchment paper or lightly grease it.
Prepare the potatoes: Wash and cut the potatoes into small, evenly sized pieces. Add them to a large bowl and toss with olive oil, garlic powder, paprika, salt, and black pepper.
Add the vegetables: Add the chopped bell peppers, zucchini, and red onion. Drizzle with the remaining olive oil and sprinkle with Italian seasoning. Toss until everything is evenly coated.
Add the sausage: Slice the sausage into bite-sized rounds and add it to the bowl. Gently toss everything together.
Arrange on the baking sheet: Spread the sausage and vegetables evenly across the baking sheet. Keep everything in a single layer so the ingredients can roast properly.
Roast: Place the pan in the oven and roast for 30–40 minutes. Toss everything halfway through cooking.
Check for doneness: The potatoes should be fork-tender, the vegetables should have browned edges, and the sausage should be heated through. If using raw sausage, make sure it reaches the appropriate safe internal temperature.
Garnish and serve: Remove from the oven and let it cool for a few minutes. Sprinkle with dried or fresh parsley and Parmesan if desired. Serve warm.