Preheat your oven to 400 degrees F. Grease your baking pan with a little butter.
Gently rinse mushrooms in cold water and brush off dirt (or wipe it off with a paper towel). Pat mushrooms dry and cut out the stems with a small knife. Chop up the stems.
Peel and finely chop four cloves of garlic.
In a 12-inch skillet, melt two tablespoons of butter. Add the garlic and cook it for a minute before adding in the mushroom stems. Stir to combine and cook the mixture for five minutes or until tender. Remove the stem mixture to a plate and spread it out to cool.
In a medium mixing bowl, add your cream cheese and stir it to break it up and soften it. Add ¼ cup mozzarella, ¼ cup Parmesan, two basil leaves cut into ribbons, your lemon zest, pepper, salt, garlic powder and Worcestershire sauce. Add in your mushroom stem mixture. Stir with two spoons to mix well.
Melt four tablespoons of butter in the microwave or in a small pan on the stove. Brush some butter all over each mushroom cap, including the top, bottom and sides. (You will have extra melted butter left to pour over the top later.) Place the mushroom caps into your baking pan.
Use a small scoop or two teaspoons to scoop some cream cheese filling into each mushroom cap. Try to smooth over the top. Sprinkle your remaining mozzarella on top of the mushroom caps. Pour your remaining melted butter over the mushrooms.
Bake for 15-17 minutes, or until the tops are just starting to get golden.
Top the mushrooms with ribbons of basil and squeeze a little lemon juice over them. Let the mushrooms rest for five minutes before serving.
Store leftovers in the refrigerator for up to five days. To prepare these ahead of time, stuff your mushrooms and refrigerate them, but hold off with the melted butter until just before baking them.