Preheat oven to 375ºF. Spray a baking dish with non-stick spray.

Cook Italian sausage over high heat for about 5 minutes, or until browned and fully cooked, using the spatula to break up the sausage.

Transfer the cooked sausage to a large bowl and allow to cool for 5 minutes. Add the panko bread crumbs and parsley leaves, and mix well.

Remove the stems from the mushrooms and set aside (they would be great for a homemade vegetable broth!). Stuff the mushrooms with the sausage mixture and place in a baking dish. Bake at 375ºF for 12-15 minutes, until the mushrooms are cooked and the sausage topping is nice and crispy. Serve immediately.