In a small saucepan, combine the diced apples, honey, cinnamon, and salt. Cook over medium heat, stirring occasionally, for 15-20 minutes, or until the apples are soft and tender.
While the apples cook, prepare the oats. In a large bowl or container with a lid, stir together the rolled oats, milk, chia seeds, and apple pie spice until well combined.
Once the apples are cooked, set aside about one-quarter of the mixture for topping. Fold the remaining cooked apples into the oat mixture.
Cover the bowl of oats and the reserved apples. Refrigerate both for at least 4 hours, or preferably overnight.
When you are ready to serve, stir the oats well. If the mixture is too thick, add a splash of milk to reach your desired consistency.
Spoon the overnight oats into bowls or jars. Top with the reserved apple mixture, a dollop of yogurt, a sprinkle of toasted walnuts, and a drizzle of honey.