If you're not using onions in your stuffing, what can you substitute to keep it moist?

An egg, whipped with a splash of water before adding.

Onions don't contribute a significant amount of moisture to stuffing. If you're worried about your stuffing drying out, try stock (chicken or turkey), egg, or melted butter. Chopped apples would be a great onion-like addition (in terms of texture).

Celery is another option, although the flavor will obviously be different.

Hi Stella! Maybe try leeks or shallots? Or even an onion bread if you still want the flavor.