Line a baking sheet with parchment paper; set it aside.
Put all of the meatball ingredients into one large mixing bowl. With your bare hands, blend until everything is well distributed.
Using a spoon, scoop up about two tablespoons worth of the meat mixture and roll it into a ball. Place the meatball onto the parchment-lined baking sheet. Repeat this until the entire mixture has been used up.
Transfer the tray into the fridge; chill for 30 minutes. (This will let the meatballs set so that they don't fall apart.) Now, get your sauce started.
Heat the oil in a deep pan over medium-low. Add the onions and the garlic, and sauté until they're softened and fragrant—about 3-5 minutes. Next, stir in the tomatoes, salt, oregano, and bay leaf. (If using a Parmesan rind, add that now as well.)
Let the sauce come to a simmer and then simmer on low for about 20-30 minutes, partially covered. If you want a smoother sauce, run an immersion blender through it until you get the texture you desire. (I partially blend mine so it's smoother but still has some chunky tomatoes present.) After 20-30 minutes is up, stir in the grated parmesan cheese.
When the meatballs are ready to come out of the fridge, carefully transfer them to the simmering sauce one by one. Spoon a bit of sauce over them and partially cover the pan again, letting the meatballs simmer on low until cooked through with an internal temperature of 160-165º F.