Preheat oven to 400°F (200°C) and line a rimmed baking sheet with parchment paper.

Clean the mushrooms with a damp paper towel to remove any grit. Gently twist and pop off the stems. Finely chop enough stems to make 1/4 cup and discard remaining stems.

Brush the outside of each hollowed mushroom cap lightly with olive oil and arrange cap-side down on the prepared baking sheet.

In a medium bowl, combine softened cream cheese, grated Parmesan, minced garlic, chopped mushroom stems, chopped parsley, melted butter, onion powder, black pepper, and salt. Mix until thoroughly blended and creamy.

Fold in half of the panko breadcrumbs (reserve the rest for topping).

Generously spoon or scoop the filling into each mushroom cavity, mounding slightly on top. Sprinkle the tops with remaining panko breadcrumbs and a pinch of extra Parmesan for a crispy golden crust.

Bake for 18 to 20 minutes until the mushrooms are tender and juicy, and the tops are golden brown and bubbling.

Let rest on the pan for 3 minutes before transferring to a serving platter. Garnish with fresh chopped parsley and serve warm!