Bring all ingredients except cauliflower to a boil over medium heat. Simmer for 5 minutes. Add the cauliflower florets and simmer gently for 1 minutes (keep them crunchy). Transfer florets with liquid and onions to a sterilized Mason jar. Close with a sterilized lid. Refrigerate for at least 3–4 hours before using.
Note: The cauliflower can be kept for up to 2 weeks in the fridge.