Fill a pot with water and bring to a boil. Add the cauliflower, reduce heat and simmer until tender- about 5 minutes. You want it to be tender enough to slide a fork through, but not mushy. Alternately, you can steam the cauliflower. Drain, and let cool. Cut into bite-sized pieces and put in a large bowl.
Add the celery and onion to the bowl too.
In a small bowl, whisk together the mayonnaise, mustard, apple cider vinegar, salt, pepper and garlic powder. Add the dressing to the bowl, and toss to combine.
Refrigerate until ready to serve.
Notes
Light mayonnaise wa used in the calculation of the nutritional information and WW points.