Heat a large saucepan or casserole dish over a medium heat and add 2 tablespoons olive oil.
Once the oil is shimmering, add the chopped onion, carrots and celery and cook, stirring occasionally, for 5-7 minutes, until the vegetables are tender and fragrant.
Stir in the garlic and dried oregano and cook for about 1 minute, until the garlic is fragrant.
Pour in the chopped tomatoes with their juices and the vegetable stock, stir to combine, then bring to the boil.
Reduce the heat to low, cover and simmer for 10 minutes to allow the flavours to develop.
Add the ditalini pasta and cook, uncovered, for 8-10 minutes, stirring occasionally, until the pasta is al dente.
Stir in the spinach and cook for 1-2 minutes more, until it has wilted into the soup.
Season with salt and black pepper, to taste, and adjust if necessary.
Ladle into bowls and serve hot with grated Parmesan and crusty bread, if you like.