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.
02 - In a small bowl, toss the diced apple with lemon juice, cinnamon, and maple syrup until the apple pieces are well coated.
03 - In a separate bowl, mix together the rolled oats, chopped nuts, melted butter, brown sugar, and cinnamon. Work the mixture with your fingers or a fork until it forms a crumbly texture.
04 - Divide the oat base evenly between two jars or containers. Layer the apple mixture on top of the oats in each jar, then sprinkle the crumble topping over the apple layer.
05 - Secure the lids on the jars and refrigerate for at least 6 to 8 hours, allowing the oats to soften and the flavors to meld.
06 - Enjoy cold straight from the fridge, or let sit at room temperature for a few minutes. For a warm option, microwave briefly for 30 to 45 seconds.