Finely chop the onion, celery, carrot and red pepper.
Heat the oil in a large saucepan and gently sauté the chopped vegetables for about 8 minutes, then add the garlic & dried herbs and cook for another 2 minutes.
Meanwhile, roughly chop the tomatoes and courgette.
Add these to the pan, then add the stock and bring to the boil. If you’re using water, add some salt.
Cook for about 10 minutes, then process it with a hand-held blender. You can add some fresh herbs too, such as basil, parsley, coriander, dill etc. The sauce can be smooth or rustic (a bit textured). If it’s too thick, add more stock (you could add more stock after defrosting it, if you’re planning to freeze bathes for later use).