Preheat oven to 375°F (190°C). Line a baking sheet with parchment paper.
Prep the mushrooms: Clean mushrooms with a damp paper towel. Remove stems and finely chop them. Set caps aside.
Make the filling: Heat 2 tablespoons olive oil in a skillet over medium heat. Add chopped mushroom stems and garlic. Sauté for 3-4 minutes until softened and moisture has evaporated.
Combine ingredients: In a bowl, mix sautéed mushroom stems and garlic with panko breadcrumbs, Parmesan, parsley, thyme, rosemary, and cream cheese (if using). Season with salt and pepper. The mixture should be moist but hold together.
Stuff mushrooms: Brush mushroom caps with remaining 1 tablespoon olive oil. Spoon filling generously into each cap, mounding slightly. Sprinkle extra Parmesan on top.
Bake: Arrange stuffed mushrooms on prepared baking sheet. Bake for 18-20 minutes until mushrooms are tender and tops are golden brown.
Serve: Garnish with fresh parsley and serve warm.