01 - In a medium bowl, combine the rolled oats, milk, Greek yogurt, chia seeds, maple syrup, ground cinnamon, and vanilla extract. Stir thoroughly until all ingredients are evenly incorporated and the mixture is well blended.
02 - In a small bowl, toss the diced apple with fresh lemon juice, ground cinnamon, and maple syrup. Coat the apple pieces evenly to prevent browning and infuse the spiced sweetness throughout.
03 - In a separate bowl, combine the rolled oats, chopped walnuts or pecans, melted butter or coconut oil, brown sugar, and ground cinnamon. Mix together until the ingredients form a crumbly, cohesive texture.
04 - Divide the oat base evenly between two jars or airtight containers. Spoon the apple layer on top of the oat base in each jar, then sprinkle the crumble topping generously over the apples.
05 - Seal the jars or containers tightly with lids and refrigerate for at least 6 to 8 hours, allowing the oats to absorb the liquid and the flavors to meld together.
06 - Enjoy cold straight from the refrigerator, or let sit at room temperature for a few minutes. For a warm and cozy variation, briefly heat in the microwave for 30 to 60 seconds.