Preheat your oven to 375°F and lightly grease a baking dish with cooking spray.
Clean the mushrooms with a damp paper towel and carefully remove the stems, setting the caps aside and finely chopping the stems.
Heat 2 tablespoons of olive oil in a skillet over medium heat and sauté the chopped mushroom stems and garlic for 3-4 minutes until softened.
Remove from heat and let cool slightly, then mix in the cream cheese, mozzarella, half the Parmesan, parsley, onion powder, salt, and pepper.
Brush the mushroom caps with the remaining tablespoon of olive oil and arrange them in your baking dish, cavity side up.
Spoon the filling generously into each mushroom cap, mounding it slightly.
In a small bowl, mix the panko breadcrumbs with the remaining Parmesan and sprinkle over the tops of the stuffed mushrooms.
Bake for 18-20 minutes until the mushrooms are tender and the tops are golden brown. Serve warm and watch them disappear!