Chop up cucamelons in a food processor and dump out into a glass or ceramic bowl.
Sprinkle the Himalayan salt on top, over the chopped cucamelons.
Cover bowl with cling wrap and put in fridge for 2-4 hours.
In a large pot, mix the apple cider vinegar, sugar, celery seed, turmeric, and mustard seed.
Bring to a gentle boil on medium-high heat.
Add the cucamelon mixture from the fridge, stir, and bring to a boil.
Reduce heat to medium-low, cover, and let simmer for 10-30 minutes, depending on amount of liquid present.
If you feel there's too much liquid after 10-30 minutes, allow it to keep boiling and stir regularly to keep it from burning.
Fill stock pot with water and bring to a boil. Add jars and lids. Boil for 10-15 minutes. (You may want to do this while relish is simmering.) Carefully remove jars from water with tongs or jar lift.
Use a slotted spoon to fill jar and cover in liquid.
Remove lids from water and add lid to the jar, securing with band.
Set jar aside to cool or add back to boiling water bath for 10-15 minutes (I didn't do this and the jars sealed fine, but apparently you're supposed to).