Cook the frozen cauliflower according to the package directions until tender-crisp.
Drain thoroughly to remove all excess water and set aside to cool completely.
While the cauliflower cools, prepare the dressing.
In a large mixing bowl, combine the chopped hard-boiled eggs, onion, celery, mayonnaise, dill relish, yellow mustard, and liquid stevia.
Stir until everything is evenly mixed.
Gently fold the cooled cauliflower florets into the dressing mixture until they are well-coated.
Season generously with salt and freshly ground black pepper to your liking.
Cover the bowl and refrigerate for at least 2 hours to allow the flavors to meld together.
Serve chilled.