Peel and core the mushrooms, then place them on a baking tray lined with baking paper.
Chop the onion very small then fry it gently in the oil for 10 minutes. Keep the heat low-medium so that the onion cooks but doesn't brown.
While the onion is frying, chop the chorizo into very small pieces.
Add the chorizo to the pan and cook with the onion for a further 10 minutes or so.
Meanwhile, chop the pasley very finely and grate the parmesan cheese.
Once the onion has become translucent, add the wine to the pan. Turn up the heat a little and cook off the alcohol.
Sprinkle the mushrooms with salt & pepper and some of the cheese. Keep some cheese aside for garnishing.
Mix the chopped parsley and breadcrumbs into the pan. This should make the mixture very dry.
Fill the mushrooms with the mixture then cover and bake at 180C (365F) for 30 minutes.
After 30 minutes, remove the foil and bake uncovered for a further 10 minutes. Remove from oven.
Chop & steam the spinach.
Serve the mushrooms on a bed of steamed spinach, topped with the remaining grated parmesan cheese & parsley.