Preheat the oven to 350°F (175°C) and grease a baking sheet with cooking spray.

Clean mushrooms with a damp paper towel. Break stems from mushrooms, chop stems into fine pieces, and set mushroom caps aside.

Heat vegetable oil in a skillet over medium heat. Cook chopped mushroom stems and minced garlic until their moisture evaporates, without burning the garlic (3-5 minutes).

Transfer the cooked mushroom mixture to a bowl. Let it cool for 10 minutes. Mix cream cheese, Parmesan cheese, black pepper, onion powder, and cayenne pepper into the cooled mushroom mixture until well combined.

Fill each mushroom cap with the stuffing mixture using a small spoon, and arrange the prepared caps on the greased baking sheet.