Chop vegetables: Pulse cabbage, green tomatoes, onions, and bell peppers in a food processor until finely chopped.
Salt vegetables: Mix chopped vegetables with pickling salt in a large bowl, cover, and refrigerate overnight.
Drain and rinse: Drain vegetables in a colander and rinse well under cold water to remove excess salt.
Prepare pickling liquid: Combine vinegar, sugar, mustard seeds, celery seeds, turmeric, ginger, and red pepper flakes in a large pot.
Simmer spices: Bring pickling liquid to a boil over medium heat, then simmer for 5 minutes, stirring to dissolve sugar.
Add vegetables: Stir in drained vegetables and simmer for 15-20 minutes until tender and well-seasoned.
Sterilize jars: Boil 6 pint jars and lids in water for 10 minutes, keeping warm until ready to fill.
Fill jars: Ladle hot chow chow into sterilized jars, leaving 1/2-inch headspace, and wipe rims clean.
Seal jars: Place lids on jars, screw on bands fingertip-tight, and process in a boiling water canner for 15 minutes.
Cool and store: Remove jars, cool for 12-24 hours, check seals, and store in a cool, dark place.