In a bowl, combine the first 10 ingredients. Crumble turkey over mixture and mix well. Remove and discard stems of portobello mushrooms. Fill mushrooms with turkey mixture.
Place in an 8-in. square baking dish coated with cooking spray. Cover and bake at 350° for 30 minutes. Uncover; bake 10-15 minutes longer or until mushrooms are tender and a thermometer inserted into stuffing reads 165°.