Place peaches in freezer until nearly frozen, 2-3 hours. Thaw 10 minutes before next step.
Add peaches, water, vanilla sugar, vanilla extract, lemon zest, and sea salt to a food processor or blender. Pulse to combine. Blend until a smooth sorbet forms. In a large bowl, alternate layers of ice cream and sorbet. Use a spatula to gently combine, just until a swirl forms. Pour sherbet into a loaf pan and gently smooth out with spatula. Place in freezer for at least 1 hour before serving.
Scoop into serving bowls. Garnish with lemon zest. Store covered in freezer for up to 2 weeks.