Prepare the Water Bath: Place a large canning kettle full of water over high heat. Add 7 clean 1-pint canning jars. There's no need to sterilize the jars, but they should be hot when you fill them.

Process: Transfer the coarsely chopped onions, bell peppers, and hot peppers to a food processor. Pulse until finely chopped.

Simmer: Combine the processed vegetables, corn, vinegar, sugar, salt, mustard, celery seed, and turmeric in a large stainless steel pot or enamel-lined Dutch oven. Bring to a boil over medium-high heat, then reduce the heat to low and simmer for 15 minutes.

Fill the Jars: Spoon the relish into the hot jars, leaving 1/2-inch headspace. Wipe rims and jar threads with a damp towel. Fit the jars with the lids. Screw the bands on the jars just to fingertip tightness.

Process in Water Bath: Place the filled jars on a rack in the canning kettle and lower them into the water. If the water level isn't at least 1 inch above the jars, add more very hot or simmering water to the pot. Bring back to the boil, cover the pan, and boil gently for 15 minutes.* Remove the jars to a rack to cool. If a jar doesn't seal properly, refrigerate it and use it before the others. Store the sealed relish in a cool, dark place.

Serve: Serve alongside a meal, as a topping, or as an appetizer spread. Enjoy!