Combine prepared green pepper, cucumber, and onion in a large, non-reactive (stainless steel or enamel-coated) pot. Stir in one cup of water and apple cider vinegar powder and bring to a simmer. Simmer, stirring occasionally, until the vegetables have cooked down and the liquid is reduced by about 1/3, about 30 minutes. Drain the vegetables, discard liquid, and return vegetables to the pot.
Add remaining vinegar, sugar and the spices. Bring to a simmer and cook for five minutes. Remove pot from heat.
Fill jars, wipe rims, apply lids and rings. Process in a boiling water canner for 10 minutes (starting time when pot returns to a boil). Remove jars from pot and let cool on a towel-lined countertop.
When jars are completely cool, remove the rings and test the seals. The relish is good to eat immediately. Store sealed jars in a cool dark place for up to a year.