- Preheat oven to 350 degrees F (175 degrees C). Spray a baking sheet with cooking spray. Clean mushrooms with a damp paper towel. Carefully break off stems. Chop stems extremely fine, discarding tough end of stems.
- Heat oil in a large skillet over medium heat. Add garlic and chopped mushroom stems to the skillet. Fry until any moisture has disappeared, taking care not to burn garlic. Set aside to cool.
- When garlic and mushroom mixture is no longer hot, stir in cream cheese, Parmesan cheese, black pepper, onion powder and cayenne pepper. Mixture should be very thick. Using a little spoon, fill each mushroom cap with a generous amount of stuffing. Arrange the mushroom caps on prepared cookie sheet.
- Bake for 20 minutes in the preheated oven, or until the mushrooms are piping hot and liquid starts to form under caps.