Preheat your oven to 375°F (190°C); then, in a medium bowl, combine the softened cream cheese, grated Parmesan cheese, minced garlic, chopped parsley, finely chopped mushroom stems, salt, and pepper, mixing until well combined.

Carefully fill each mushroom cap with the cream cheese mixture, ensuring it is mounded nicely.

In a small bowl, toss the breadcrumbs with melted butter; then, sprinkle the buttered breadcrumbs over the filled mushroom caps.

Place the stuffed mushrooms on a baking sheet and bake for 18-20 minutes, or until the mushrooms are tender and the topping is golden brown.