Put the cauliflower and beans in a large bowl and cover with boiling water. Stand for 2 minutes, then drain and refresh under cold water. Add the corn kernels, red pepper and onions, and mix to combine. In a small non-reactive pan, combine the remaining ingredients and bring to a simmer. Pour the pickling mix over the veg and leave to pickle for 15 minutes (see Make Ahead).
The quick pickled veg will keep, covered in the fridge for 5 days. Add left overs to sandwiches or serve with cold cuts of meat.