This salad is best made in August when peaches are at their best!
For the dressing - combine the basil, olive oil, vinegar, honey, mustard and shallots in a blender until the dressing emulsifies and the basil is pureed. Season with salt and pepper.
Combine the tomatoes, peaches, basil and onion slices in a bowl and toss to coat with the dressing. Top with the feta cheese. Serve at room temperature.