For the kielbasa:
Preheat the oven to 350 degrees F.
While the sauce is cooking, heat the oil over medium heat in a large skillet. Cook kielbasa until they begin to brown being careful to keep heat at medium so they don't split. Transfer to a large baking dish with a slotted spoon, reserving the drippings in the skillet to sear the meatballs.
For the meatballs:
While the kielbasa are cooking, mix breadcrumbs, milk, onions, eggs, and parsley in a mixing bowl. Add ground beef and mix thoroughly. Form into small meatballs and sear in the pan in which the kielbasa were cooked. Transfer with a slotted spoon to the baking dish with the kielbasa. Pour the sauce over the kielbasa and meatballs, and cover with a lid or foil, and finish in the oven for about 20 minutes.
Serve as sandwiches with Italian rolls.