Coarsely grate the courgette into a large bowl. Pat dry with kitchen towel to remove as much excess liquid as possible. Add the pork mince, half the spring onions and the egg yolk. Combine well, using your hands, then shape the mixture into 24 little balls.
Heat the oil in a large, deep-sided frying pan (preferably non-stick). Cook the meatballs in batches for 5-8 minutes or until golden all over.
Transfer the meatballs to a plate, and set aside. Add the remainder of the spring onion to the pan along with the carrot and thyme. Cook this mixture for 5 minutes, stirring occasionally, until the onion has softened slightly. Add the tomatoes.
Boil 150ml water in a kettle and add to the tomato purée in a cup, then pour into the pan. Return the meatballs to the pan, bring to the boil, cover and reduce the heat to simmer for 15 minutes.
Serve the meatballs immediately with the cooked macaroni and a sprinkling of parmesan, if liked.