Place the peppers into a large pot. Add vinegar, water, spices, and onion (optional). Bring to a boil, then reduce heat to medium-low, and simmer for 5 minutes.
Ladle peppers into sterile jars, fill to the top with the liquid (leave 1/4 inch headspace). Process jars in water bath.
Store up to 12 months in pantry and refrigerate jars after opening.