To make the dressing, combine olive oil, vinegar, Dijon, salt, and pepper in a small bowl or jar. Whisk or shake together until smooth.
Spread arugula out on a plate or platter, then arrange sliced peaches, blueberries, and prosciutto on top. Drizzle lightly with spoonfuls of dressing (you may not use it all), scatter pine nuts and basil on top, and serve.
Notes
Pine Nuts: You can buy pine nuts already toasted at Trader Joe's and many other grocery stores, but you can also toast raw pine nuts yourself. To do so, place them in a small skillet over medium heat and cook for 2-3 minutes, stirring very frequently, until golden brown in spots. Remove from the heat, let cool, and use as desired.