Place the cucmbers into the food processor and pulse briefly unti finely chopped. Measure out 4 cups of the chopped cucumbers and place in a bowl.
Place the bell peppers into the food processor and pulse briefly unti finely chopped. Measure out 2 cups of the chopped bell peppers and add to the cucumbers.
Place the onion into the food processor and pulse briefly unti finely chopped. Measure out 2 cups of the chopped onion and add to the cucumbers.
Add the kosher salt and stir to combine well. Cover the mixture with ice water and set aside for 2 hours.
Drain in a colanderthen rinse well. Drain and squeeze out any excess moisture.
In a large stock pot or dutch oven, combine the sugar, vinegar, celery seed and mustard seed. Bring to a boil.
Add the drained vegetables, stir and simmer for 10 minutes.
Add the relish to sterilized hot jars, leaving room for expansion (about 1/4 inch).
Top with lids and rins to just hand tight.
Add jars to boiling water and process for 15 minutes. Remove from water and set aside to cool.
