||Preheat oven to 350°F.
||In a large skillet heat butter or olive oil over medium-high heat; add onion and mushrooms and saute until golden and mushrooms begin to darken and dry out (about 15 minutes). Remove from heat and cool 15 minutes; season with salt and ground black pepper, if desired.
||In a large bowl combine sour cream, mayonnaise, 1/3 cup cheese, and parsley; mix well. Dice chicken strips and fold into cooled mushroom-onion mixture, mix thoroughly.
||Spread mixture evenly in a 1 quart casserole dish and sprinkle the top evenly with remaining cheese.
||Bake 25-30 minutes or until completely heated through, bubbling and cheese is melted on top. Remove from heat and serve while hot.