Slice the chorizo on the diagonal and place the slices in a large, heavy-based frying pan over a medium heat. Cook gently for 4-5 minutes, turning halfway through, until the oil begins to escape from the sausage.
Drain the mozzarella ball(s) and slice into discs about ¼" (0.5cm) thick. Lay the slices on top of the chorizo, then spoon some of the beautiful red oil from the bottom of the pan over the top. Cook for 2-3 minutes to allow the cheese to melt, then season with a few twists of freshly ground black pepper.
Slice the baguette along one side and either open up or pull apart. Spoon the chorizo and mozzarella into the baguette, then spoon those wonderful chilli and paprika juices from the bottom of the pan over the top (absolutely no need for any butter since the pan juices will make the bread deliciously moist).
Place a handful of spinach leaves on top, close the baguette and give it a gentle squeeze. This will allow all of the juices to soak into the bread, and the spinach to wilt a little. Cut the baguette into four and serve immediately.