Preheat the grill to medium heat.
Brush the cut sides of the peach halves with a little olive oil.
Place the peaches cut-side down on the grill and cook for about 4-5 minutes, until grill marks appear and the peaches are slightly softened. Remove from the grill and let cool slightly.
In a large bowl, combine the mixed salad greens, blueberries, and crumbled feta cheese.
In a small bowl, whisk together the olive oil, balsamic vinegar, honey, salt, and pepper to create the dressing.
Slice the grilled peaches into wedges and add them to the salad mixture.
Drizzle the dressing over the salad and gently toss to combine.
Top with toasted walnuts before serving.