Preheat oven to 350. Grease a 15 x 10 jelly-roll pan. Clean mushrooms, removing stems;set caps aside. Finely chop enough mushroom stems to equal 1/2 cup. In a large skillet, melt 6 tablespoons butter over medium heat. Add mushroom stems,green onion,capers,thyme,salt and pepper;cook 5 minutes,stirring frequently, or until stems are tender. Stir in chicken and wine;cook 5 minutes,or until wine has evaporated. Add cream cheese and panko,stirring until combined. Fill mushroom caps evenly with the chicken mixture. Place in pan,and brush each with melted butter. Bake 20 minutes. Serve immediately. Makes about 2 1/2 dozen.