Prepare the Vegetables: Wash and chop cucumbers, bell pepper, and onion. Mix with salt and let sit for 1 hour.

Drain Excess Liquid: Use a strainer to remove excess liquid, pressing gently with a spoon.

Make the Brine: Combine vinegars, sugar, mustard seeds, celery seeds, turmeric, and chili flakes in a pot. Heat until sugar dissolves.

Combine Everything: Stir the vegetable mix into the brine and simmer for 10 minutes.

Jar the Relish: Ladle hot relish into sterilized jars, leaving ½ inch headspace. Seal tightly.

Process for Preservation: Process jars in a boiling water bath for 10 minutes.

Cool and Store: Let jars cool for 24 hours before storing in a cool, dark place.