In a mixing bowl, combine the rolled oats, chia seeds, ground cinnamon, and a pinch of salt. Stir well to combine.
In a separate bowl, mix the milk, vanilla extract, and maple syrup until well blended.
Pour the milk mixture over the oat mixture and stir gently to combine.
Fold in the Greek yogurt for a creamier texture, if using, then add the raisins or pecans.
Divide the mixture into jars or airtight containers. Seal them tightly and refrigerate overnight (or at least 4 hours) to allow the oats to soak and soften.
In the morning, give the oats a good stir. If desired, drizzle with additional maple syrup and sprinkle with extra cinnamon for a finishing touch.
Serve cold or warm in the microwave for a short time if preferred.
Notes
For a creamier texture, include Greek yogurt. Customize with your choice of nuts or dried fruits.