Put beans into a pot, covered with water and salt. Bring to a boil, then reduce to simmer for 15 minutes. Set aside when done.
If using chard, remove the hard stems from the leaves. Reserve the stems for another use, or discard.
Heat olive oil in a pot and add chard or spinach leaves. Salt slightly. Stir periodically until the leaves begin to wilt, approximately 3-5 minutes. Then cover, reduce heat to low, and continue cooking for approximately 10 minutes, stirring periodically to avoid burning. Set aside when done.
Make the meatballs by combining all meatball ingredients in a bowl. Roll them into balls about 2 inches across (a bit smaller than a biliard ball).
In a pot, combine the beans, chard or spinach, meatballs, onion, garlic, and tomato sauce. Add water to just barely cover. Gently insert eggs around the top of the stew. Bring to a boil, then reduce heat.
Continue cooking overnight by any standard method (slow cooker, pot in a low oven, or pot on an electric hotplate, for example).