Fry the onion until its clear approx 4 to 5 mins and allow to cool.
In a bowl add the mince, cold onions, beaten egg, cumin, Parmesan, crushed garlic, tomato paste and breadcrumbs and mix well. Season with the salt and pepper. I use my hands to mix rather than a fork/spoon. Make into meatballs and set aside. Heat the oven to 200 degrees C / 180 C fan forced.
Heat the the oil in a frypan to medium heat and add the meatballs. Fry off the meatballs until they are brown on the outside.
Add the pasta sauce to the meatballs, still keeping on a medium heat and cook for about 10 mins..
Transfer everything to a baking dish and tear the mozzarella into pieces and add to the dish, scattering the pieces around the meatballs.
Cover the dish and cook in the oven for about 20 mins. Then take off the lid and cook for a further 10 to 15 minutes.