Toast the oats. Pre-heat oven to 180°C (350°F). Pour oats onto a baking tray and spread out evenly. Bake in the oven for 20 minutes, stirring halfway through, until toasted and golden. Remove from the oven and set aside.
Toast the hazelnuts and de-skin them. Place hazelnuts onto a separate baking tray and bake for 15 minutes. (The tray can go into the oven at the same time as the oats). Remove the hazelnuts tray from the oven and allow to cool slightly. Using a paper towel, tea towel or between your fingers, rub the hazelnuts, and the skins will come off easily. Do this until the majority of the skins have been removed. Divide the hazelnuts in two and roughly chop half the hazelnuts and set them aside.
Make the paste. In a food processor, add the dates, peanut butter, maple syrup, coconut oil, water, salt, and whole hazelnuts, and whizz up until a paste has been created.
Mix toasted oats and hazelnuts together. Into a large mixing bowl, add the toasted oats, cocoa powder, and remaining chopped hazelnuts and stir until fully combined.
Add date mix to the dry ingredients. Scoop the date mix into the mixing bowl with the oats and use a wooden spoon, rubber spatula or even your hands to incorporate the paste into the oats thorougly.
Prepare your baking pan. Line a 23cm (9x9-inch) square baking pan with parchment paper. To help it stick, add a couple of dabs of butter to the base and sides of the pan. Let the paper overhang to use as a sling later.
Add to prepared pan and refrigerate. Pour the mixture into the prepared pan and using the back of a spoon or your fingers, press the mixture down firmly until it’s level and fairly compact. Refrigerate for a couple of hours until the bars are firm.
Cut and decorate. Lift the bars out of the pan using the paper overhang. Slice the square in half and then each half into 6 bars. To serve, melt the dark chocolate in 20 second increments in the microwave. Stir after each burst. Drizzle the melted chocolate over the top of the bars.