This is not the no-mess, super-easy recipe of yore, but it is low in fat and high in flavor. To go one step further, substitute 1/2 pound fresh green beans for frozen. Simply trim and cut into 1-inch lengths. Then blanch the beans for 1 to 2 minutes in boiling water, refresh under cold water and spread in the baking dish.
Make Ahead Tip: The onion topping, toasted breadcrumbs and sauce can be prepared ahead and stored in separate containers, covered, in the refrigerator for up to 2 days.