Preheat the grill to medium heat. Brush the cut sides of the peach halves with olive oil.
Place the peaches cut-side down on the grill and cook for about 4-5 minutes, or until grill marks appear and the peaches are slightly softened. Remove from the grill and let cool slightly.
In a small bowl, whisk together honey, salt, and black pepper.
In a large bowl, combine the mixed salad greens, fresh blueberries, and crumbled feta cheese.
Slice the grilled peaches into wedges and add them to the salad mixture.
Drizzle the honey dressing over the salad and toss gently to combine.
If desired, sprinkle chopped walnuts on top for added crunch.
Serve immediately, drizzled with balsamic vinaigrette.