Preheat the oven to 375 degrees F. Spray a 13 by 9-inch baking dish with nonstick cooking spray.
In a large skillet, melt the butter over medium-heat. Add the mushrooms and saute until browned, 7 to 8 minutes. To the skillet, add the sour cream, chicken soup, almonds, poppy seeds, and chicken. Pour the chicken mixture into the prepared baking dish.
In a small bowl, combine the melted butter and crackers; sprinkle over the chicken mixture. Cover with aluminum foil and bake about 15 minutes. Uncover and bake until bubbly, about 10 minutes longer. Serve over rice, if desired.
Recipe courtesy of Paula Deen