In a large mixing bowl, combine the rolled oats, almond milk, grated apple, chia seeds, cinnamon, maple syrup, Greek yogurt (if using), and a pinch of salt.
Stir the mixture until all ingredients are well combined and the oats are fully submerged in the liquid.
Divide the mixture into two or three jars or containers with airtight lids.
Seal the jars and refrigerate overnight (or for at least 6 hours) to allow the oats to absorb the liquid and soften.
In the morning, stir the oats and add a splash more almond milk if you prefer a creamier consistency.
Top with chopped nuts and an additional sprinkle of cinnamon before serving.
Notes
Add more almond milk in the morning for a creamier texture.