Heat 1 tsp olive oil in a pan. Add the onion and garlic with some seasoning and the chilli flakes.
Cook for 5 minutes and then add the celery, carrot, ½ the parsley and courgette. Fry for 5 minutes more. Tip in the tomatoes and break up slightly with a wooden spoon. Add the stock and simmer for 10 minutes.
In a separate pan, cook the tortellini following the pack instructions. Add to the soup, stir well then serve with the remaining chopped parsley.