Bake the butternut squash (do this ahead). Cool completely before using.
Checkout in this recipe how to bake the butternut squash: Marbled Crustless Butternut Squash Cheesecake (High-Protein Cottage Cheese Bake). Alternatively use red kuri squash and bake it as explained here: Easy Roasted Red Kuri Squash (Hokkaido Pumpkin)
Mash the butternut squash. Mash the cooled, baked butternut squash until smooth.
Mix the overnight oats. Add the rolled oats, Greek yogurt and milk to the squash mixture. Stir until everything is thoroughly combined and no dry oats remain. Then stir in the cinnamon and the maple syrup.
Refrigerate overnight. Transfer the mixture to a 16-ounce (475 ml) wide-mouth glass jar or airtight container. Cover and refrigerate for at least 4 hours, preferably overnight, until the oats are soft and creamy.
Prepare the apple. Just before serving, wash and coarsely shred the apple. Keep the skin on for extra color and texture. If it releases a lot of juice, gently squeeze out the excess.
Add the toppings and serve. Remove the oats from the fridge and add your fresh toppings. Spoon the shredded apple into a fluffy mound right in the center of the jar for a beautiful presentation. Scatter the chopped pecans around the apple base, drizzle with sweet maple syrup, and finish with an optional pinch of cinnamon before diving in.