Bring a large pot of salted water to boil. You'll use this to blanch all the veggies in.
Blanch the cauliflower first - cook for 1 minute, then use a skimmer to remove it all and place it in a large mixing bowl. Then blanch the cabbage and cucumber for 30 seconds, then remove them with the skimmer to the mixing bowl. Lastly, blanch the pepper and onion for 5 seconds, then remove them to the mixing bowl. Toss all the veggies together.
Mix the flour, mustard, salt, turmeric, sugar, and 1 cup of the vinegar in a saucepan, and bring to a boil. Reduce heat, and then simmer for 3 minutes. Add in remaining vinegar and cook for 10 minutes or until thickened.
Spoon the veggies into 4 1-pint jars, and pour the hot vinegar mixture over the top. Let cool, then store covered in refrigerator for up to a month.