Put the porridge oats in a saucepan and mix in half of the cinnamon. Add the (oat) milk, then turn on the heat.
Simmer over low heat for 10 minutes. Add a little more milk, if needed. Turn off the heat, give it a stir, then put a lid on and rest for 5 minutes.
Meanwhile, peel the bananas then slice them - not too thinly! Drizzle some lemon juice over them and set aside.
Heat a non-stick pan and dry-fry the walnuts. Set aside.
In the same pan, heat the maple syrup, vanilla and the lemon juice. When it starts sizzling add the banana slices and cook them for about one minute on each side, until they lightly caramelise.
Spoon the porridge into two bowls, add some vanilla yogurt and top with the banana and maple syrup sauce.
Scatter the walnuts over the bananas and drizzle with more maple syrup, if desired.
Serve warm.