Lightly spray a 20cm square tin with cooking spray and line with baking paper.
In a medium size saucepan, combine peanut butter, choc chips, maple syrup, coconut oil, salt and cinnamon. Warm the pot on a low-medium heat, stirring continuously, until the mixture is melted and combined. Remove from heat.
Stir in the vanilla extract, followed by the oat flour, desiccated coconut and the walnuts.
Put the mixture into the tin and spread using the back of a spoon. Sprinkle the salt flakes on top (if using) then cover and refrigerate for 2-3 hours (you can also freeze for 30-45 minutes if you require a quicker result.)