Preheat oven to 425F (use Convection if you have it). Line a baking sheet with aluminum foil for easier cleanup if desired.
Add the sausage, potatoes, onions, evenly drizzle with olive oil, evenly seasoning with the Italian seasoning, salt, pepper, and toss with your hands to combine and coat evenly.
Bake for about 40 to 45 minutes, or until potatoes are tender and have as much color as desired; toss halfway through baking to ensure even cooking. Start checking at 30 minutes for doneness since all ovens, veggies, etc. vary.
Optionally sprinkle with Parmesan and serve immediately.