Heat the olive oil in a large saucepan, add the chorizo and cook for 2 minutes. Add the chopped onion and garlic and season, then sweat over a gentle heat for 7-8 minutes, until soft. Add the tomatoes, stock and herbs, if necessary season again with salt, pepper and a good pinch of sugar and simmer with the lid on for another 10 minutes or until the tomatoes are soft.
Add the pasta and continue to simmer for another 6-10 minutes, stirring regularly or until the pasta is cooked. When you are ready to serve, drop in the spinach and boil for just 1 minute or until the spinach is wilted. Taste for seasoning. To serve, ladle the chunky soup into large warm bowls and sprinkle with some finely grated Parmesan and a drizzle of pesto.