Find two 2-cup reusable containers with lids such as jars. In each of the containers, place half the oats at the bottom of the jar and half the brown sugar, cinnamon and nutmeg. Pour half the milk into each container.
Peel 2 bananas and slice, roughly 1 cm thick; divide banana slices equally among containers.
Top each container with half the yogurt. Cover tightly with lids; refrigerate overnight (or for 8 hours).
Serve cold, mixed or unmixed with optional toppings of additional yogurt, brown sugar and walnuts.