Prep Mushrooms: Clean the mushrooms and remove the stems. Chop the stems finely into small pieces and set aside.
Cook Pork: Heat a non stick saute pan over medium and then add the oil. Add the pork and saute, breaking up into small pieces as it cooks. Saute for about 5 minutes, and then remove from the pan and set aside to cool. The pork will finish cooking in the oven with the mushrooms. Deglaze the pan with the chicken stock, scraping up the cooked bits as it deglazes.
Preheat Oven: Preheat oven to 375℉ and place rack in the middle.
Saute Filling: Once most of the chicken stock has been cooked off, add the onion and garlic and saute for 1-2 minutes, stirring often. Add the finely chopped mushroom stems and saute another 2-3 minutes. Add the salt, pepper, rosemary, and parsley and mix well. Finaliy, add the panko breadcrumbs and saute for another 2 minutes.
Mix Cheeses: Add the cream cheese to a large mixing bowl. Soften the cream cheese slightly by microwaving for 15-20 seconds. Add the mozzarella and parmesan and mix well.
Mix Filling: Add the pork and sauteed mushroom stem filling to the bowl with the cheese and mix well, ensuring that it is all thoroughly mixed together.
Stuff Mushrooms: Use a small spoon to add a little bit of the filling to the mushroom cap and gently press it down into the cap. Add another larger spoonful to top of the mushroom cap and gently press to shape it together in a small mound. Place on baking tray and repeat with the rest of the mushrooms and filling.
Bake: Bake for 20 minutes.
Serve and Enjoy: Garnish with more minced parsley and serve warm.