Cut stems off the bell peppers, and slice the ends off the onions and zucchini. Put the zucchini, onions, and bell peppers through the food processor. Dump them in a non-metallic bowl and pour the salt over the top. Use your hands to mix the salt in evenly.

Cover the mixture with saran wrap and refrigerate overnight.

The next day, drain the mixture in a colander - rinse with water, squeeze excess, rinse again, and squeeze out the excess.

Combine the sugar, vinegar, mustard seeds, turmeric, black pepper, celery seed and nutmeg in a medium stockpot. Mix well until sugar is dissolved, then bring to a boil. Immediately reduce the heat to low/medium and simmer 4-5 minutes.

Add the zucchini/onion/pepper mixture to the stockpot, stir to distribute spices/vinegar evenly. Bring to a boil, then immediately reduce the heat to low/medium and simmer 25-30 minutes.

In the meantime, sterilize 6 pint canning jars and lids in your water bath canner. Remove and set aside. Ensure the water bath canner is filled at least half way with water to process the jars once filled.

Ladle the relish into your jars, leaving 1/2 inch of head space. Screw the lids and bands on tightly, and rinse the jars under the faucet to remove any relish residue.

Place the jars in the water bath canner - ensure they are not touching, and that they have at least 2 inches of water covering the tops of the jars. Bring your water bath canner to a full boil, then cover and process for 30 minutes.

Carefully remove the jars, place on a cloth covered counter top until cool 24 hours.

Push on the top of each jar lid to ensure a tight seal. The lid shouldn't move up and down (if it does, you may need to re-process longer in the water bath).

Jars can be stored in a cool, dark pantry for up to 8 months. Once opened, refrigerate and use within 2 weeks.