Steam cauliflower until fork tender—about 12 minutes. Remove cauliflower from steamer and run under cold water to stop cooking. Drain well, and combine in a large mixing bowl with the eggs, celery, red onion and dill pickle.

In a small bowl, whisk together the mayo, Greek yogurt, mustard, salt and pepper. Pour dressing over cauliflower mix, and toss to coat. Cover and chill for at least an hour before serving.