Preheat grill to medium.
Peel and section the grapefruit with a pairing knife over a small bowl to capture any juice. Once you have removed all sections squeeze the grapefruit to extract any left over juice into the bowl. Place sections into a separate bowl. Cut peaches into 1/8ths and brush with oil. Grill for 5 minutes until slightly soft.
In the bowl with the grapefruit juice add the honey, oil, salt and pepper and whisk until well combined. In a large salad bowl add arugula, grapefruit, grilled peaches, sliced scallions and vinaigrette. Toss well to combine and serve.