Put the porridge oats into a pan and add the cinnamon. Mix well, then add the oat milk. If time allows, let the oats soak for about 10 minutes.
Turn the heat on and cook over low heat for 10 minutes. It should be creamy - add a little more milk, if needed. Turn off the cooker, give it a stir, then put a lid on and rest for a few minutes.
Meanwhile, make the stewed apples. Peel the apple, then core and dice. Put them in a small pan and add the remaining ingredients. Bring to a boil and cook for about 5 minutes or until the apple gets soft but not mushy. Turn off the heat and set aside.
Spoon the porridge into two bowls, add the stewed apple, then scatter some walnuts on the top.
Serve with a dollop of (plant-based) vanilla yogurt, if liked.