Place the onion into the Thermomix bowl and chop on Speed 6, 5 seconds. Scrape down the sides and repeat. Add all remaining meatball ingredients and mix on Speed 5, 15 seconds. Scrape down the sides of the bowl and mix for a further 10 seconds.
Roll into 1 tablespoon-sized balls and place into a baking/casserole dish. Cook in the oven for 20 minutes.
While the meatballs are cooking, make the tomato sauce by placing the onion and garlic into a clean Thermomix bowl. Chop on Speed 6, 10 seconds. Scrape down the sides and repeat if needed.
Add the olive oil and saute for 2 minutes, 80 degrees, Speed 2. Add the remaining sauce ingredients and cook for 20 minutes, Varoma, Speed 1.
When the meatballs have cooked for 20 minutes, pour the tomato sauce over the top and grate over the cheese. Bake for the final 15 minutes. Serve.
If you can't get panko breadcrumbs, you can use traditional breadcrumbs.