I have been making these for years.
I don't throw away the mushroom stems, I chop them up. After you cook the bacon, use some of the grease and saute the stems, garlic and 1/4 cup of chopped onion until the onion is translucent. Mix it into the cream cheese and skip the parsley. Stuff the mushrooms with the mixture and dip in the shredded cheddar cheese so it sticks to the top. Bake them at 350°F for 25 minutes.
For a real special treat, freeze the mushrooms for about an hour. Take them out of the freezer and dip them in a good batter and deep fry them until golden brown. Make sure not to overcook them or the cheese will spew out. Drain and enjoy.