Method:
Preheat oven to 400°F. Toss sweet potatoes with onion, black pepper and 1/4 teaspoon cinnamon in a medium bowl. Transfer to a parchment-paper-lined baking sheet and roast until tender, about 45 minutes.
Meanwhile, whisk together vinegar, honey, remaining 1/4 teaspoon cinnamon and chives in a medium bowl. Toss together arugula and radishes in another medium bowl. To serve, arrange arugula mixture on plates. Toss sweet potatoes in balsamic mixture and spoon over arugula.