Preheat oven to 350°F. Finely chop enough mushroom stems to measure 1 cup; discard any remaining stems. Place mushroom caps, rounded-sides down, in lightly greased shallow baking pans.
Cook sausage, chopped stems and garlic in large skillet over MEDIUM-HIGH heat 8-10 minutes or until sausage is thoroughly cooked, stirring frequently; drain. Return to skillet. Add cream cheese, 1/2 cup breadcrumbs, 1/4 cup Parmesan cheese and parsley; mix well. Spoon into mushroom caps.
Combine remaining breadcrumbs, remaining Parmesan cheese and oil; sprinkle over mushrooms.
Bake 20 minutes or until mushrooms are tender and stuffing is lightly browned.