This simple casserole is a quick preparation, and it makes a fabulous family dinner. Serve it with a salad or sliced tomatoes, or add rice or pasta to your menu. If you're cooking for a larger group, double the recipe and bake it in a 13-by-9-by-2-inch baking pan. We topped the casserole with soft bread crumbs we pulsed in the food processor, but it could be topped with fine dry breadcrumbs or panko crumbs tossed with melted butter. To make it ahead, layer the spinach and chicken with sauce and then cover the dish and refrigerate for up to 24 hours. When you're ready to bake it, preheat the oven, top with the buttered breadcrumbs, and bake