Prepare the balsamic vinaigrette: In a small bowl or jar, whisk together the olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper until well combined. Set aside.

Assemble the salad base: In a large bowl, combine the baby arugula, sliced peaches, fresh mozzarella, and thinly sliced red onion.

Add the dressing: Drizzle about half of the prepared balsamic vinaigrette over the salad ingredients. Toss gently to coat everything evenly.

Adjust seasoning and add nuts: Taste the salad and add more dressing if desired. Sprinkle with toasted pecans if using.

Serve immediately: Divide the salad among plates and serve right away for the best flavor and texture.