Preheat oven to 350°. In large skillet, saute onion in butter 3 to 4 minutes or until lightly browned. Add tomato sauce, chilies, cilantro, chili powder and salt. Simmer, uncovered, 5 minutes. Layer half the following ingredients in buttered 1 1/2 quart casserole in this order; tortilla chips, Monterey Jack cheese, chicken and tomato sauce mixture; repeat layers. Bake 25 minutes. Remove from oven; spread sour cream over top of casserole. Sprinkle with Cheddar cheese. Return to oven 5 minutes or until heated through and cheese is melted. Garnish with fresh cilantro or parsley.