Add the instant oats to a small bowl. Add the walnuts and cinnamon and mix.
Next add the non-dairy milk, vanilla, and maple syrup and mix until well combined.
In your mason jar, start by layering 3-4 slices of banana at the bottom. Add about 1/4 to 1/3 of the oat mixture on top in an even layer. Repeat with remaining ingredients until jar is almost full (but not too full where the lid won't go on properly), then carefully place lid and band.
Repeat for as many servings as you'd like to make.
Refrigerate oats overnight, and enjoy as soon as the next morning! I found that as long as the jars stayed sealed, they lasted in the fridge for about a week.
Notes
A dollop of non-dairy yogurt on top makes this even more decadent, even dessert-worthy!