Preheat the oven to 350°F (180°C).
Remove the stems from the mushrooms. Finely chop half of the stems, and either discard the remaining stems or reserve them for later use. Brush the top of the mushroom caps with olive oil and place on a lined baking tray.
Finely mince the chorizo in a food processor and set aside.
Place a large skillet over medium heat and add the olive oil. When the oil is heated, add the minced chorizo and sauté until the meat is turning golden and releases the fat, about 3 minutes.
Add the mushroom stems, diced onion, and bell pepper and continue to cook for another 3 minutes, stirring constantly.
When the onion turns transparent, add the garlic and breadcrumbs and fry until the breadcrumbs become golden brown.
Take the skillet off the heat and gently spoon the chorizo and breadcrumb mixture into the mushrooms to create little mounds.
Bake for 25 minutes, or until lightly browned on top. Garnish with fresh parsley leaves and serve immediately.