Add the avocado, cacao, sweetener and salt to a food processor or high-speed blender and blitz until smooth and creamy.
Very gently melt the coconut oil and chocolate in a pan, then add to the processor. Pulse to combine.
Transfer the mix to a container, then pop into the fridge for a couple of hours to firm up so that you can easily roll the truffles.
Scoop out bite-sized pieces of the truffle mix and roll into balls in your hands, then roll in some cacao. Store in the fridge or freezer.
Scoop out bite-sized pieces of the truffle mix and roll into balls, flatten with your hand, insert a whole hazelnut into the centre, then fold the truffle around the nut. Roll in your hand to create a round ball.
Add the chopped hazelnuts to a plate, then roll the truffles in the nuts. Store in the fridge.