Slice your bread into one-inch cubes and spread them out on a baking sheet. Bake at 350ºF for 15 minutes until toasted and crisp.
Meanwhile, pit and slice your peaches into wedges. Chop your tomatoes into one-inch pieces. Transfer the peaches and tomatoes to a colander fitted over a bowl to allow the juices to drip out.
In a small bowl, add your Dijon mustard, honey, and balsamic vinegar and whisk until combined. Slowly drizzle in olive oil while whisking to incorporate it into the balsamic mixture. Season with salt and pepper to taste.
In a large bowl combine the tomatoes, peaches, red onion, mozzarella, and sliced basil.
Add the toasted bread cubes to the large bowl, then drizzle with vinaigrette, tossing to coat.
Allow the panzanella salad to rest for 30 minutes before serving, tossing occasionally if you can. Season with salt and pepper and a little bit more fresh basil before serving.