Preheat a grill pan to medium-high heat.
For the dressing: Combine the rice wine vinegar and Dijon in a small bowl. Slowly pour the olive into the bowl, whisking constantly to emulsify. Season with salt.
For the salad: Place the peaches in a bowl and drizzle with olive oil. Sprinkle with salt and toss well. Place on the grill and cook for 1 to 2 minutes on each side.
Place the mesclun mix in a large bowl. Add chopped pecans, feta and cooked peaches. Drizzle salad with dressing and toss to coat.