Preheat the oven to 350°. Lightly grease a jelly-roll pan.
In a large skillet cook the bacon over medium heat until crispy. While the bacon cooks, use a clean dish towel to wipe the mushrooms clean. Remove the stems and coarsely chop them. Place the caps on the baking sheet.
Once the bacon is crispy, drain it on paper towels and then crumble it. Pour away all but 2 tablespoons of the remaining bacon grease.
Return the skillet with the remaining bacon grease to the heat. Add the chopped mushroom stems and cook until they are tender. Pour the cooked mushroom stems into a large bowl, and add the crumbled bacon, cream cheese, garlic powder, onion powder,
and Parmesan cheese. Stir gently to combine. Spoon about 1 tablespoon of the filling into each of the mushroom caps. Bake 18 to 20 minutes or until the filling is heated through.