1Heat the oil in a large pan, add the onions, and cook over low heat for 6-8 minutes or until soft.
Season with sea salt and freshly ground black pepper, then add the garlic, rosemary, celery, and carrots and cook over low heat, stirring occasionally, for 10 minutes.
2Add the zucchini and cook for 5 minutes, then stir in the tomatoes and squash them with the back of a fork.
Add the stock, bring to a boil, then reduce to a simmer and cook for 20 minutes.
Season with salt and pepper, then stir in the parsley.
3Let cool completely, then transfer to as many freezer-proof containers as you wish, seal, and freeze for up to 3 months.
4To serve, defrost in the refrigerator overnight, then transfer to a pan and heat until piping hot.
Serve with crusty bread.