Using a channel knife or citrus stripper, remove the zest from the lemons, creating long strips of peel. If you don't have a channel knife, use a vegetable peeler and slice the peel into thin strips.
Bring a pot of water to a boil. Add the lemon zest, boil briefly, then strain. Repeat this blanching process five times to remove most of the bitterness while preserving the bright citrus flavor.
Transfer the blanched lemon zest to a heatproof container.
Combine the rice wine vinegar, sumac, red chili flakes, coriander seed, black peppercorns, bay leaf, brown sugar, and kosher salt in a saucepan. Bring to a gentle simmer until the sugar dissolves.
Remove the pickling liquid from the heat and stir in the ice to cool it slightly. Pour the pickling liquid over the lemon zest, then refrigerate until completely chilled.