Combine chopped cucumber, onion and bell pepper in a large Dutch oven or stockpot.
Mix in salt and add cold water to cover. Let soak for 2 hours. Thoroughly drain in a colander.
In the rinsed and dried stockpot, combine vinegar, sugar, mustard seed, celery seed and turmeric. Bring to a boil and then add drained vegetables.
Bring relish to a simmer and cook for 10 minutes.
Pack into hot, sterilized jars leaving 1/4-inch headspace. Remove air bubbles, clean rims of jars and attach two piece lids. Process in a boiling water bath for 10 minutes.
Let sit for 2 weeks in the pantry before opening to allow flavors to blend.