Pre-heat a barbecue or grill pan to medium-high heat.
Place the potatoes in large bowl and toss with about 3 tablespoons EVOO, 2 tablespoons grill seasoning and the rosemary. Grill the potatoes on a barbecue or grill pan for 4-5 minutes on each side.
While the potatoes are cooking, combine the oranges and red onion and dress with red wine vinegar and some EVOO.
Remove the potatoes from the grill or grill pan to the dressed oranges and onions and toss to coat. When you grill the potatoes, they will be slightly drier than when you use other methods of cooking. By adding the potatoes to the dressing while they are hot, they really will soak in the dressing.
When you are ready to serve, add the arugula to the potatoes and toss to distribute.