Makes enough for a 1 gallon jar or 8 pint jars.
Wash and slice the peppers, onions, and cucumbers. Pack into a gallon jar until it is full, or layer into pint jars. Sprinkle with mustard seeds, if desired.
Combine the brine ingredients in a small pot. Heat to dissolve, and pour into jar (will only be 1/2 full). Don't seal; refrigerate at least 3 days before eating, or to taste. Keep refrigerated.
Note: Becky also used mustard seeds in her pickles (just a few sprinkled on top), as well as a bit of apple cider vinegar in the brine for some extra kick.