Place julienned radish in a colander or mesh sieve and hold over sink. Carefully pour boiling water over the radish to soften them, allowing the water to simply drain through.
Carefully transfer warm radish to a clean 1 pint mason jar.
In a separate bowl (or measuring cup with spout ideally) combine the apple cider vinegar, ½ cup water, salt and sugar until all is dissolved and well combined.
Pour liquid mixture over radish and intermingle the peppercorns.
Place lid on mason jar and refrigerate ideally for 1 day before using (but at least 4 hours).
The pickled radish will store well in the sealed mason jar in the fridge for a week or longer.
Notes
Prep & Storage: you simply need a clean 1 pint (500 ml) mason jar (no sterilization required) to make these but they need to be stored in the refrigerator. They will last in the sealed mason jar in the fridge for a week or more. The Vinegar: apple cider vinegar (diluted to 5% acidity) works perfectly here - imparting a really nice flavor without the sharp acidity. Cutting the Radish - it's surprisingly simple to julienne the radishes - cut the end bits off, slice each fairly thin and then cut the disks (circles) into match sticks. It only took a few minutes. Warming the Radish - running boiled water over the radish facilitates absorption of the brine and seasonings.
Recipe by Inspired Edibles at https://www.inspirededibles.ca/2019/06/tangy-quick-pickled-radish-zincs-avo-toast.html