Heat the oven. Preheat to 400°F. Line a large rimmed sheet pan with parchment if you like an easy cleanup.
Toss the vegetables. Toss sweet potatoes, apples, and onion with olive oil, salt, and pepper, and spread in a single layer.
Add the sausage and drizzle. Nestle sausage links among the vegetables. Whisk maple syrup and Dijon and drizzle over the pan.
Roast, then flip. Roast for 20 minutes, then turn the vegetables and sausage.
Finish and check. Roast for 20 minutes more, until sweet potatoes are tender and sausage reaches 160°F in the center.