In a large skillet, saute celery, green pepper and onion in butter until tender; remove from the heat. Add chicken, rice, broth, peas, pimientos, salt and pepper; mix well. Spoon into a greased 13-in. x 9-in. baking dish.
Combine soup and mayonnaise; spread over chicken mixture. For topping, combine stuffing and almonds; sprinkle over casserole. Drizzle with butter.
Cover and bake at 350° for 30 minutes. Uncover and bake 15 minutes longer or until bubbly.