01 -
Combine the sliced bell peppers and onions in a large mixing bowl to evenly disperse the vegetables.
02 -
In a medium saucepan, add white vinegar, apple cider vinegar, granulated sugar, mustard seeds, celery seeds, turmeric powder, salt, ground black pepper, and red pepper flakes. Place over medium heat and bring to a boil, stirring until the sugar is fully dissolved.
03 -
Carefully pour the hot pickling solution over the mixed bell peppers and onions. Stir thoroughly to ensure all vegetables are coated with the liquid.
04 -
Allow the mixture to cool to room temperature. Transfer the relish to clean, airtight containers or glass jars, ensuring the vegetables are fully submerged in brine.
05 -
Place the containers in the refrigerator and let the relish rest for a minimum of 24 hours to enable the flavors to meld before serving.