01 - In a medium mixing bowl, combine the rolled oats, milk, Greek yogurt, chia seeds, maple syrup, cinnamon, and vanilla extract. Stir thoroughly until all ingredients are evenly incorporated and the mixture is well blended.
02 - In a separate small bowl, toss the diced apple with fresh lemon juice, ground cinnamon, and maple syrup. Gently fold until the apple pieces are evenly coated and begin to soften slightly.
03 - In another bowl, combine the rolled oats, chopped nuts, melted butter, brown sugar, and cinnamon. Use your fingers or a fork to work the mixture until it forms coarse, pea-sized crumbs.
04 - Divide the oat base evenly between two jars or airtight containers. Spoon the seasoned apple mixture over the oat layer in each jar, then sprinkle the crumble topping generously over the apples.
05 - Seal the jars or containers tightly with lids and refrigerate for a minimum of 6 to 8 hours, allowing the oats to absorb the liquid and the flavors to meld together.
06 - Enjoy straight from the refrigerator cold, or let sit at room temperature for 10 minutes. For a warmer option, microwave briefly in 30-second intervals until heated through to your liking.