Grease a 20cm square cake tin and line with baking parchment. Tip the cashew nuts and oats into a food processer and blitz to crumbs. Add the dates and coconut oil, and blend again. Transfer to the tin and use a spoon to press the nutty mixture into a compact, even layer that covers the base. Chill while you prepare the filling.
For the filling, add the dates, almond milk, maple syrup and coconut oil to a saucepan with a generous pinch of salt and bring to a simmer. Boil for 2-3 mins until the dates are really soft, then tip into the blender, add the vanilla extract and blitz to a smooth purée. Add a little more salt if the mixture is too sweet. Pour over the nutty base and spread to the sides of the tin, getting the surface as smooth as possible. Chill while you prepare the topping.
Gently heat the coconut oil in a saucepan until melted. Remove from the heat and whisk in the cocoa and maple syrup until there are no lumps. Cool for 10 mins, pour over the caramel layer and return to the fridge for at least 3 hrs or until firmly set. To serve, cut into squares. Will keep in the fridge for up to 1 week.