Mix all ingredients in a large bowl, except cubed cheese.
Using an ice cream scoop (approx. 1/4 cup), form a ball. Insert a cube of mozzarella cheese and wrap meatball around cheese.
Line a cookie sheet with foil and spray lightly. Place formed meatballs on sheet and bake at 400 degrees for approx. 15–20 minutes.
Serve with spaghetti sauce or place meatballs in slow cooker with sauce on LOW for 3–4 hours or on HIGH for 1–2 hours.
In a sauté pan, heat oil and onion and sauté until onion is translucent. Stir in garlic and stir approx. 30–60 seconds. Add all the remaining ingredients; bring to a slow simmer, cover, and continue to simmer for approx. 3–4 hours.
When cooled a little, use an immersion blender or when very cool, blend in blender until desired consistency. Serve with meatballs.
Recipe courtesy of Mary Kolodziej, Stevens Point, WI.