Slice the florets off the cauliflower, breaking them into pieces the size of the tip of your little finger. Discard the branches and core.
Over medium heat, bring the vinegar, sugar and salt with one quart of water to a light boil in a large saucepan.
Add the cauliflower, onions, and cabbage. Cook four or five minutes. Add the green tomatoes and red bell pepper and cook two or three minutes. Turn the heat off and let the vegetables cool in the boiling liquid for about a half-hour.
While waiting, drain the pickles and chop them into small dice (about 1/4 inch) by hand. When the vegetables are cool, drain and chop them about the same size as the pickles.
Combine the pickles and vegetables in a large bowl. Add the mustard and stir to blend.
Sterilize canning jars of whatever size you prefer. Fill the sterilized jars with the chow-chow mixture. Cap and process according to standard canning procedure. It's best to let the chow-chow rest for a week or more before using.