Preheat oven to 350 degrees. Foil and grease a large baking sheet, set aside.
Prepare the mushrooms by wiping away any dirt with a damp cloth. Carefully pull out the stem of each mushrooms and set stems to the side. Use a small spoon to scrape out the mushroom gills.
Toss the mushroom caps in a large bowl with the oil and a few pinches each of salt and pepper. Place the mushroom caps onto the prepared baking sheet.
Roughly chop both the mushroom stems and spinach into small pieces.
In a large skillet, cook the bacon. Remove the bacon and add the mushroom stems, spinach, green onion, garlic powder, parsley and black pepper to the skillet. Cook over medium heat for about 5 minutes.
In a large bowl, combine the mushroom mixture with the softened cream cheese. Crumble the bacon and add it to the bowl. Mix well.
Stuff each mushroom cap with about 1 tablespoon of the cream cheese mixture.
Combine the remaining 1 teaspoon of parsley flake with the parmesan cheese and panko bread crumbs. Top each mushroom cap with the parmesan mixture. Drizzle the mushrooms lightly with olive oil.
Bake mushrooms for 12-15 minutes or until golden brown.