Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C). Spray a baking sheet with cooking spray.

Wipe mushrooms with a damp paper towel; carefully remove stems. Chop stems extremely fine, discarding the tough end of stems.

Heat oil in a large skillet over medium heat. Add garlic and chopped mushroom stems; fry until any moisture has evaporated, taking care not to burn garlic. Set aside to cool.

Stir in cream cheese, Parmesan cheese, black pepper, onion powder, and cayenne until well combined.

Use a teaspoon to fill each mushroom cap with a generous amount of stuffing. Arrange mushroom caps on the prepared baking sheet.

Bake in the preheated oven until mushrooms and filling are piping hot, about 20 minutes.

Serve and enjoy!