Preheat oven at 200C.
Melt ½ the butter & heat up 1 tbsp olive oil in a frying pan.
Add the onions, garlic, oregano, salt & pepper to the pan. Cook for 4 minutes over medium to high heat, stirring occasionally.
Add the cherry tomatoes, tomato paste & Worchestersshire sauce to the pan. Cook for 3 minutes over medium heat, stirring occasionally.
Add the tomato sauce to the pan & bring to boil. Simmer for 20 minutes.
In a bowl, mix the minced meat, salt, pepper, meat seasoning, curry, paprika, garlic powder & celery.
Form the meatballs & set them aside.
In another frying pan, heat up 1 tbsp olive oil & melt the rest of the butter.
Cook the meatballs for 5 minutes over medium to high heat, turning them as they brown on each side.
When done cooking the meatballs, put them in an oven dish & pour the tomato sauce over them.
Cover the dish with aluminium foil & cook in the oven for 30 minutes.
Uncover the dish & add the mozzarella on top of the meatballs. Cook in the oven for 5 to 10 minutes.