These are amazingly moist and delicious.  I’ve swapped out traditional tomato sauce in these meatballs for salsa verde (you can make your own or use Trader Joe’s which has no preservatives or thickening agents).  The onion (red onion is my preference, but use whatever you have on hand) also lends moisture.  I use 85/15 beef as I find anything with less fat just becomes too dry.