Chunk up your cucumbers by slicing them into about ¾" thick slices and cutting these in halves or quarters, depending on how large your cucumbers are. Cut up peeled onions into ½" to ¾" dice and cut the cauliflower into bite-size florets. Place all of the veg in a large pot or non-reacitve bowl that you can place a weighted plate over to press down the veg.
Sprinkle the veg with the coarse sea salt and stir well to combine. Place a plate on top of the salted veg, inside the pot or bowl, and weigh it down with cans or any other heavy object(s). Leave this to sit overnight to draw out the moisture.
The next day, fill a large pot with water, so that the water comes about an inch above your jars when placed on a wire canning rack or round cooling rack in the bottom of the pot. Add the jars, open side up so that they fill with water. Bring to a boil and sterilize for 10 minutes before removing them and placing them in a pre-heated oven at 225°F to remain warm while you prepare the pickles. Repeat as necessary until all jars are sterilized.
While waiting for the canning water to boil, drain the released moisture from the veg through a callander, in batches, giving a slight rinse to remove some of the salt. Drain well and place on clean tea towels to dry.
We used 580 ml Weck canning jars, as seen in one of the photographs, and sterilized all of the lids in a separate medium-sized pot. You can do the same with standard sealing lids. After 10 minutes, turn off the heat. Remove the lids and place them in the oven with the jars. Place the rubber seals or snap lids in the pot of boiling water and remove from the heat to allow the rubber to soften up.
Combine the vinegar, sugar and bag of pickling spices in a medium sauce pot and bring to a boil before reducing to a simmer to dissolve the sugar. Continue to simmer for approximately 5 minutes.
Add the diced tomatoes and mustard to the vinegar mixture and bring to a boil before reducing to a simmer for another 5 minutes or so.
Combine the flour, turmeric and water and mix into a paste. Add this paste to the mustard mixture and bring to a boil before reducing to a simmer to thicken.
Add the veg mixture to the sauce and heat to just before boiling, before filling prepared canning jars. It is important to fill and seal the jars as quickly as possible once the veg is heated, to ensure that it stays crispy.
Once all of the jars are filled and sealed, process the jars for 10 minutes in the same canning bath pot used to sterilize the jars. Remove them and allow to cool on the counter before storing in a cool dry place.