Combine apple and brown sugar in a small bowl. Mix well.
Microwave apples for one minute, then stir. Cook for another 30 seconds, or until apples are softened and tender. (Mine took 1 ½ minutes total.)
Add half the apples, along with the oats, milk, half the walnuts, maple syrup, cinnamon, vanilla, and salt, to a mason jar. Mix well.
Top oats with remaining apples and walnuts. Cover and refrigerate overnight, or for at least 4 hours, before eating. Enjoy!
Notes
I recommend using crisp, tart-sweet apples, like Fuji, Gala, Pink Lady, or Honey Crisp (which is what I used) for this recipe.Any kind of milk works here, although 2% or whole will give you the creamiest results.To make the recipe vegan, use a vegan brown sugar and any kind of non-dairy milk, such as almond milk. I used soy milk, which worked great.Check out the info before the recipe for more tips and variations.