Preheat the oven to 375°F. Arrange the mushroom caps on a baking sheet and drizzle them evenly with the olive oil.
In a mixing bowl, combine the cream cheese, spinach, garlic, Parmesan cheese, breadcrumbs, salt, and black pepper until the mixture is smooth and evenly blended.
Spoon the filling into each mushroom cap, pressing gently so it stays in place.
Bake the mushrooms for 20 minutes until the tops turn lightly golden and the filling is hot throughout.
Remove from the oven and sprinkle the chopped parsley over the tops before serving.