Preheat the oven to Gas Mark 4 (350F degrees). Line a 8 x 10 inch oven safe dish with baking parchment (leave a generous overhang on all sides) & set aside.
In a large saucepan, gently cook the chopped apples over a very low heat, stirring often, until about half of them have broken down. I usually leave a lid on the pan, stirring every 2-3 minutes - if you are easily distracted like me, put a timer on repeatedly! The apples should release enough juice while heating that they don't stick to the bottom of the pan, just remember to keep an eye on them.
In a small bowl, mix the cornflour into the maple syrup until there are no clumps remaining, then stir in the ground cinnamon.
Once the apples start to break down add the maple syrup mixture, stir together thoroughly, then set aside to cool slightly.
In a large bowl, combine together the oats, flour, brown sugar and cinnamon. Drizzle the melted coconut oil in and mix together until everything is coated in the oil.
Stir in the lightly beaten egg - this helps to bind the oats together as they are baking.
Spoon about ¾ of the oat mixture into the lined oven dish and press down firmly. Layer the apple mixture on top and finish by crumbling the remaining oat mixture on top.
Cook for 30 - 35 minutes or until the streusel is lightly browned on top. Allow to cool in the dish on a wire rack, then refrigerate until completely cold.
Remove from the dish (the baking parchment overhang helps in removing the bars once chilled). Cut into bars and serve hot or cold, drizzled with a little cream or even caramel sauce if liked.
Bars will stay fresh for 3 days in an airtight container in the fridge, or will happily freeze for up to 2 months.