Start by washing and dicing your apple into small, bite-sized pieces. If you prefer a smoother texture, you can grate the apple instead. In a wide-mouth mason jar or a small container with a lid, add the rolled oats, chia seeds, ground cinnamon, and a tiny pinch of salt. Stir these dry ingredients together to ensure the cinnamon and chia seeds are evenly distributed.

Pour your chosen milk, Greek yogurt, maple syrup, and vanilla extract into the jar. Stir the mixture vigorously with a spoon, ensuring you scrape the bottom of the jar so no dry oats are left behind. Once the base is creamy and well-combined, gently fold in the diced or grated apples.

Seal the jar tightly with its lid and place it in the refrigerator for at least 6 hours, though overnight is best for the creamiest texture. During this time, the oats and chia seeds will absorb the liquid and soften. In the morning, give the oats a quick stir. If the mixture is too thick for your liking, splash in a little extra milk. Top with your favorite nuts or extra cinnamon before serving cold.