Preheat the oven to 400 degrees F. Remove and discard stems from mushrooms. In a large bowl, toss mushroom caps with oil. Arrange caps rounded-side down on a parchment lined baking sheet. In a skillet over medium-high heat, cook and crumble the sausage until it is lightly browned and cooked through, about 5 to 7 minutes. Let cool.
In a bowl, combine cooled sausage, cream cheese, garlic parsley, Parmesan, breadcrumbs, salt and pepper; mix well. Spoon about 1 tablespoon of sausage mixture into each mushroom cap. Bake until mushrooms are tender, about 25 minutes. Serve hot.