1Heat oven to 350°F. Remove stems from mushroom caps; reserve caps. Discard stems. In large bowl, mix cream cheese, spinach, 1/2 cup of the Parmesan cheese, the salt and both peppers until well blended. Spoon into mushroom caps, mounding slightly. Place mushrooms in ungreased 17x12-inch half-sheet pan.
2In small bowl, mix remaining 1/2 cup Parmesan cheese, the bread crumbs and butter. Sprinkle bread crumb mixture over filled mushroom caps, pressing lightly.
3Bake 20 to 22 minutes or until thoroughly heated. Serve immediately.