Heat the oil in a heavy based casserole dish and add only half the carrot, onion, and garlic. Cook over low heat for 2 minutes until softened. Stir in passata, tomato paste and water, simmer for 5 minutes.
For the meatballs: Combine the remaining carrot, onion and garlic with mince, breadcrumbs, parsley, egg and seasonings. Knead thoroughly with your hands until the mixture is very sticky, shape the mixture into golf ball sized balls and stuff each with one cube of cheddar ensuring that the cheese is fully enclosed. (Moistening your hands with water helps here in shaping the balls).
Drop the meatballs into the simmering sauce, cook over low heat, covered for 20 minutes, stirring occasionally.
Serve meatballs sprinkled with parsley and parmesan, over spaghetti or just accompanied with seasonal vegetables or a salad.