Preheat oven to 350. Dice onion and apple. Sauté onion in a small amount of oil till semitransparent.
In a large bowl, mix the onions and apple dice with the remaining meatball ingredients. Form into meatballs using a ice cream scoop with swing lever (makes the perfect size).
Place meatballs about 1 inch apart on large oiled baking pan or cookie sheet. Cook in 350 oven for 20-30 min, checking often not to overcook as these will go into the skillet with the sauce for about 5-8 more minutes of cooking.
Combine sauce ingredients in a small saucepan. Bring to a boil; reduce heat. Simmer, uncovered for 10 minutes, stirring occasionally. Look Out! the vinegar is pungent!
Place meatballs into large skillet, add sauce and cook over low heat for 5-8 min. Stir only enough to coat the meatballs or they will want to fall apart. Can just skip this step and use as a dipping sauce... but they are so good like this!