In a bowl combine Italian sausage, 1/4 cup of Parmesan cheese, parsley, and garlic. Mix well.
Spoon a tablespoon or so of the mixture into each mushroom. Place mushrooms on a baking sheet. Drizzle lightly with olive oil. Cook for 15 - 20 minutes or until meat is cooked through.
Remove mushrooms from oven. Sprinkle with remaining cheese. Return to oven and turn on the broiler. Broil until the cheese is melted and slightly golden. About 1 minute. Serve hot.