Put cauliflower in a microwave-safe casserole, add just a tablespoon of water and cover. Cook on high 7 minutes, and let it sit covered, for another 3-5 minutes. (You may steam if you prefer.)
Drain cauliflower and combine with celery and onion. Combine the mayo, vinegar, salt, sugar, and pepper. Pour over the vegetables and mix well.
Mix in the chopped eggs last and stir lightly to preserve some small chunks of yolk. Chill and serve.