In a bowl, mix peanut butter, maple syrup and rolled oats with a rubber spatula. Melt the coconut oil in a small pot over low heat and add the peanut butter mixture to the pot. Cook for approx. 1 min.
Line the baking dish with parchment paper and spread the peanut butter oat mixture evenly into the bottom of the dish with the rubber spatula. Press firmly. Freeze for approx. 20 min.
Roughly chop dark chocolate and melt in a heatproof bowl over a pot with simmering water. Pour the chocolate over the cooled peanut butter oat mixture and spread evenly. Freeze for approx. 60 min.
Take the baking dish out of the freezer, cut the bars into equal pieces with a knife and sprinkle with flaky sea salt. Store in an airtight container in the fridge, and enjoy!