Blitz the onion and celery in a food processor to a mush, reserving two tablespoons for the meatballs.
Warm garlic oil in a heavy-based saucepan and cook remaining onion, celery, and thyme for 10 minutes.
Add 800g plum tomatoes and 800ml water to the pan, season with sugar, salt, and pepper, and simmer.
Gently mix turkey mince, egg, breadcrumbs, parmesan, Worcestershire sauce, thyme, and reserved vegetables in a bowl.
Roll the mixture into approximately 50 small balls the size of a teaspoon and place on a lined tray.
Drop the meatballs gently into the simmering tomato sauce.
Simmer the meatballs in the sauce for 30 minutes until cooked through.