Preheat oven to 350°F (175°C). Lightly grease a baking sheet with cooking spray.
In a medium bowl, whisk together cream cheese, Parmesan, garlic, green onions, salt, and pepper until smooth.
Using a small spoon or piping bag, fill each mushroom cap generously with the cheese mixture.
Arrange stuffed mushrooms on the prepared sheet. For extra crunch, sprinkle with a pinch of breadcrumbs or more Parmesan.
Bake 20–25 minutes until mushroom cups are tender and topping is golden brown.
Let cool 5 minutes before serving—perfect for a cozy snack or elegant appetizer.