Preheat the oven to 350 degrees F. Melt the butter in a saucepan over medium-high heat. Add the onion and celery and cook, stirring occasionally, until the vegetables are soft. Add the mushroom soup, chicken broth, soy sauce, and cooked chicken. Mix well and heat through. Transfer the chicken mixture to a baking dish. Top with chow mein noodles and cashews. Place the baking dish in the oven and bake at 350 degrees F for 20-25 minutes. Serve hot.