In a large mixing bowl, combine the rolled oats, almond milk, vanilla extract, ground cinnamon, and maple syrup if using. Stir well to combine all ingredients.
Gently fold in the diced peaches and Greek yogurt if you want a creamier texture.
Divide the mixture evenly into four jars or containers with lids.
Top each jar with chopped pecans or walnuts if desired.
Seal the jars 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 and enjoy cold, or warm them in the microwave for about 30-60 seconds if you prefer them heated.