Preheat an oven to 425°F.
Place Brussels sprouts on a rimmed sheet pan. In a small bowl, combine olive oil, maple syrup, Dijon mustard, black pepper, and salt. Pour this mixture over the Brussels sprouts and stir to combine.
Roast for 30-35 minutes or until golden brown and mostly tender. Add cranberries and walnuts. Return to the oven and roast for another 5-10 minutes. Watch carefully as both the cranberries and walnuts will burn if you keep them in for too long.
Remove from the oven and sprinkle the orange juice over the Brussels sprouts. Toss to combine.