In a medium bowl mix the oats, yogurt, flaxseed, sugar, vanilla extract, cinnamon, nutmeg, and milk (Alternatively, you can divide the ingredients between two jars and mix into 2 individual portions).
Cover and refrigerate for at least 2-3 hours, or ideally overnight.
When ready to serve, slice the apple into small cubes and mix in as desired (layers or mixed in) with the oats.
Garnish top with additional apple slices, or other toppings, if desired.