Sterilze four pint-size canning jars; set aside. See note.
Cut off the cucumber ends and discard. Shred cucumbers and place in a large glass (non-reactive) bowl.
Place the onions in a food processor and pulse to finely chop. Add onions to cucumbers and sprinkle with the salt. Allow to rest for 1 hour.
Drain the cucumber mixture well; rinse with cold water and drain well again.
Place red pepper, jalapeños, and garlic in a food processor; pulse until finely chopped. Set aside.
In a large pan, bring vinegar and remaining ingredients to a slow boil; simmer until sugar is dissolved.
Add cucumber/onion and red pepper/jalapeno/garlic mixtures. Return to a simmer, stirring frequently. Simmer for 10 minutes.
During this time, bring a small pan of water to a simmer.
When ready to fill the jars, place canning lids in the simmering water.
Fill each jar with cucumber mixture, leaving 1/2" of head space. Wipe the rim of the jar to clear any relish that may interfere with proper sealing. Place one sterilized lid on top and twist a canning ring on top. Ring should be secure but not overly tightened.
Repeat with other jars.
Process the jars for 10 minutes in a hot water bath.
Remove and cool completely. Ensure lids sealed before storing.