In a medium bowl or jar, combine the rolled oats, milk, chia seeds, maple syrup, vanilla extract, cinnamon, and salt. Stir well to combine all ingredients.
If using Greek yogurt, fold it into the mixture until evenly distributed.
Cover the bowl or jar with a lid or plastic wrap and refrigerate overnight (or for at least 4 hours) to allow the oats to soak and soften.
In the morning, give the oats a good stir. If the mixture is too thick, add a splash more milk to reach your desired consistency.
Top with your favorite toppings such as fresh fruit, nuts, seeds, or a dollop of nut butter before serving.