1. Halve the peaches, remove pits, and slice into ¼ inch thick slices. Wash, half, and seed the cucumber (and peel if needed). Slice the cucumber into thin slices. In medium bowl toss peaches, cucumbers, onion, and salt.
2. Heat apple cider vinegar, water, and honey in a saucepan until simmering. Pour hot liquid over the peach-cucumber mixture. Toss to combine and refrigerate overnight.