Instructions

1. Arrange 4 empty regular mouth pint jars in a canning pot or a 12-quart stock pot fitted with a round cake cooling rack. Fill the pot with enough water to cover the jars. Place a lid on the pot and bring it to a boil. Wash the lids and rings in warm, soapy water and set aside.
2. Fit a food processor with a grating blade and use it to break down the zucchini, green peppers, and onion. If you don't have a food processor, pull out your trusty box grater and get to work.
3. Combine the zucchini, pepper, and onion shreds with the vinegar, brown sugar, mustard seeds, salt, and red chili flakes in a large pot and bring to a boil.
4. Cook the relish at a boil until the liquid has reduced some, 2 to 3 minutes. Add the lemon zest and juice and stir to combine.
5. Remove relish from the heat and, using a wide-mouth funnel, funnel it into prepared jars, leaving approximately 1/2 inch headspace. After all the jars are full, use a wooden chopstick to work the air bubbles out of the jars.
6. Wipe the rims, apply the lids and rings, and lower the filled jars into the canning pot and make sure that they are covered with only about an inch of water. If you need to remove some water from the pot, use a heatproof measuring cup. Once the pot has returned to a rolling boil, start your timer for 10 minutes. This proces sterilizes the jars and contents, and it forces the air out of the jars, creating a situation in which the jars will form a vacuum seal once out of the water.
7. When time is up, remove jars from canner and place them on a folded kitchen towel to cool. When the jars have cooled enough that you can comfortably handle them, check the seals by removing the rings, grasping the jar by the edge of the lid and gently lifting it an inch or two off the countertop. If the lid holds fast, the seal is good. Sealed jars can be stored at room temperature for up to a year. Any unsealed jars should be refrigerated and used promptly.