Preheat oven to 400 degrees. Lightly grease a 9 x 13 baking dish.
Taking a damp paper towel, wipe off mushrooms. Using a small sharp knife, cut around the stem area and pop the stem off. Chop the stems into small pieces to use in the stuffing.
Place mushrooms into baking dish and baste with melted butter.
In a large skillet, heat up 1 TBS cooking oil an add diced onion. Saute until softened. Add garlic and cook for 1 minute.
Add ground italian sausage and cook until thoroughly browned.
Add chopped mushroom stems to sausage and cook for 1-2 minutes. Turn off heat.
Place cream cheese into a large bowl. Add sausage and stems, bacon bits, 1/2 shredded cheese, panko, parsley, salt & pepper. Mix well.
Using a 1 inch scoop or 1 TBS place mixture into mushrooms pressing firmly to fill. Make sure mixture also forms a dome on the top.
Sprinkle with extra 1/2 cup shredded cheese onto each mushroom and press into mixture.
Bake for 18-22 minutes until cheese is golden brown and mushroom is tender. Enjoy.