Preheat oven to 350° F and spray a cookie sheet with cooking spray. Clean mushrooms with a damp paper towel. Carefully break off stems and discard the tough end. Chop the stems extremely fine
Heat oil in a large skillet over medium heat. Add garlic and chopped mushroom stems to the skillet. Fry until all moisture has disappeared, making sure that you don't burn the garlic. Set aside.
When garlic and mushroom mixture is no longer hot, add cream cheese, parmesan cheese, black pepper, onion powder and cayenne pepper. Mixture should be very thick. Using a little spoon (I use a 1/8 tsp. measuring spoon)fill each mushroom cap with a generous amount of filling. Arrange mushrooms on cookie sheet. Bake in preheated oven for 20 minutes or until mushrooms are piping hot and liquid starts to form under caps.