Bring the milk to a boil in a saucepan. Add the quinoa and reduce the heat to a low simmer. Cover and cook for about 15 minutes, until most of the liquid is absorbed.
Remove the lid and stir in the maple syrup, cinnamon, and half of the banana. Stir and continue to cook for 5 more minutes, until all of the liquid is absorbed.
Serve hot, and top with the remaining banana and chopped walnuts.