In a small bowl, combine rice vinegar, lime juice, and shallots. Let shallots soak for at least 10 minutes.
In a large bowl, combine cucumber, peaches, avocado, basil, and mint. Add soaked shallot mixture, sumac, extra-virgin olive oil, and a few pinches of salt; toss well to combine. Taste and season with a pinch more salt, if needed.
