Combine cucumbers, onions and pepper chunks in a food processor and pulse until the chopped vegetables are chunky but not pureed (do this in batches, if needed). You should be able to see small pieces of the veggies.
In a large saucepan, combine the cucumber mixture and salt. Let sit at room temperature for 2 hours.
Use a fine mesh strainer to strain the liquids out of the relish mixture. Add the solids back to the saucepan, along with the vinegar, garlic, sugar, dill seed, mustard seed and celery seed.
Stir until combined and place over high heat. Bring to a boil. Reduce to low heat and simmer for 15 minutes, stirring occasionally.
Remove from heat and let cool for 10 minutes. Transfer to mason jars for storing and use the hot water bath method to extend the shelf life.
Notes
There is a lot of room for flavor enhancements! Add hot peppers for a spicier mixture. Use extra sugar for super sweet relish. Use extra onions and garlic for extra zing. Other fresh veggies such as carrots or zucchinis are a nice addition.
Be sure not to skip the straining part! This will ensure the consistency is not too runny.
For a less sweet relish, decrease the amount of sugar used and increase how much onion and peppers are added.