Combine oats, almond milk, chopped apple, maple syrup, butter, chia seeds, cinnamon, cornstarch, water, vanilla extract, and salt in a jar or container.
Mix well until all ingredients are evenly combined.
Cover and refrigerate overnight or at least 4 hours.
Stir the oats before serving and enjoy cold or warmed.
Notes
For extra flavor, top with nuts or additional apple slices.