Preheat your oven to 400ºF (200ºC). Lightly spray a large sheet pan with cooking spray. Spread the diced sweet potatoes and halved Brussels sprouts apart on the sheet pan. Turn the Brussels sprouts cut side down.
Drizzle everything with olive oil, sprinkle with seasoning, then add salt and pepper to taste. Roast the sweet potatoes and Brussels sprouts for 15 minutes.
Combine maple syrup and Dijon mustard in a mason jar and shake well to make the sauce.
Remove the sheet pan from the oven, and add sliced sausage, garlic, and red onion. Drizzle half the maple-dijon sauce over and toss with the veggies. Return the sheet pan to the oven and continue to roast for 15 minutes longer.
Remove the sheet pan from the oven. Drizzle the remaining sauce over the sausage and veggies and toss to coat. Sprinkle with parsley and parmesan and serve immediately.
