For the dressing:Combine the balsamic vinegar and shallot in a small bowl. Slowly pour the olive into the bowl, whisking constantly. Season with salt and pepper. For the arugula salad:Place a grill pan over medium-high heat or preheat a gas or charcoal grill. Brush the plums with the olive oil and grill for 2 minutes on each side. On the other side of the grill cook the pancetta slices on each side, until crispy, about 1 to 2 minutes.
Place the arugula in a large salad bowl. Slice the grilled plums and add to the bowl. Add the vinaigrette and toss to lightly coat the arugula. Crumble the pancetta over the top and sprinkle with the hazelnuts. Serve immediately.
*You can use any stone fruit such as peaches or apricots. Red apples or figs are also great alternatives.