In a large mixing bowl, combine all the ingredients except for mushrooms and stir delicately until well combined.
With a spoon, gently press the filling into the mushroom's cavities and create a small mound on top of each mushroom, too, without overfilling. Place the stuffed mushrooms on the prepared sheet and refrigerate for at least 30 minutes.
Preheat oven to 375°F and bake the mushrooms for approximately 20 minutes or until tops become golden brown. Let the mushrooms rest for 5 minutes then transfer them to a plate, garnish with chopped parsley and serve.