Heat the remaining 1 tablespoon oil in a large skillet over medium-high heat. Add sausage and cook, breaking it up with the back of a spoon, until browned, crumbly and no longer pink, about 4 minutes. Stir in the reserved chopped mushroom stems, scallions, garlic and pepper; cook, stirring occasionally, until the mushrooms are softened, about 2 minutes. Remove from heat and immediately add cream cheese; stir until well combined. Stir in breadcrumbs, parsley and Parmesan.