Preheat your oven to 400°F (204°C) and line a rimmed baking sheet with parchment paper. Wipe mushroom caps clean with a damp paper towel (never submerge in water). Pop out the stems and mince them finely. Heat 1 tablespoon olive oil in a skillet over medium heat. Sauté the minced mushroom stems and minced garlic for 3 to 4 minutes until golden and fragrant. Remove from heat and cool for 5 minutes.

In a medium mixing bowl, combine the softened cream cheese, grated Parmesan, chopped parsley, fresh thyme, onion powder, salt, black pepper, and the cooled sautéed garlic mushroom stems. Beat with a wooden spoon or spatula until smooth and thoroughly combined.

Brush the outside of each hollowed mushroom cap lightly with olive oil and arrange cavity-side up on the baking sheet. Generously mound 1 tablespoon of the herb cream cheese filling into each cap. In a small bowl, toss together panko breadcrumbs, melted butter, and 2 tablespoons grated Parmesan. Sprinkle the buttery panko over each stuffed mushroom, pressing gently so it adheres.

Bake for 15 to 18 minutes until the mushroom caps are tender and juicy, the filling is piping hot and melted, and the panko topping is deeply golden brown and crisp. Garnish with extra fresh chopped parsley and serve warm on a party platter.