Preheat your oven to 375°F.
Clean the mushrooms and remove the stems. Set aside the mushroom caps on a baking sheet.
In a skillet over medium heat, cook the chorizo, breaking it up with a spoon, until browned and cooked through.
Add chopped onions and garlic to the skillet. Cook until the onions are softened. Remove any excess grease if necessary.
In a bowl, combine the cooked chorizo mixture with breadcrumbs, Parmesan cheese, chopped parsley, salt, and pepper. Mix well.
Generously fill each mushroom cap with the chorizo mixture, pressing it down slightly. Place on a parchment lined baking sheet.
Drizzle olive oil over the stuffed mushrooms for added flavor.
Bake in the oven for about 15-20 minutes or until the mushrooms are tender and the tops are golden brown.
Remove from the oven and let them cool for a few minutes before serving.