Cut the cauliflowers, onions, green beans and cucumbers into bite-sized pieces then place in a large bowl, along with the chillies and sprinkle with the salt. Cover and place in the fridge overnight.
The next day drain the vegetables and rinse with cold water to remove the excess salt.
Place the vegetables in a large preserving pan with the vinegar, nutmeg, allspice and sugar. Crush the garlic with the salt and add that in too. Bring to the boil, then turn down to simmer for 10 minutes.
Take off the heat then remove the vegetables with a slotted spoon leaving the liquid behind. Pour the liquid into a separate jug and set aside for a moment.
Sift together the tapioca flour, cornflour, turmeric, ginger, curry powder, mustard powder and pepper. Add 200ml of the reserved liquid and blend together to make a smooth paste.
Pour the paste into the preserving pan and with the heat on very low, slowly pour the rest of the reserved liquid into the paste, whisking all the while.
Bring to the boil, then cook for 5 minutes or until the sauce has thickened.
Add the vegetables back into the sauce, stirring to coat thoroughly. Turn off the heat.
Decant into sterilised jars and store in a cool dark place until needed.