Sprinkle Mozzarella cheese on it and bake for 15 to 20 minutes till the top layer is golden brown.
Incorporate your choice of vegetables like bell pepper, sliced tomato, chopped celery or sliced and grilled egg plant.
Broccoli, mushrooms and other vegetables can be prepared one day in advance. All you need to make is the white sauce on the day you bake.
Images are clicked by me