Add the tahini, peanut butter, coconut sugar, oat flour and gluten-free flour to a mixing bowl. Mix together well and press into a 5 inch/14cm tartlet tin. Poke a couple of holes in the bottom using a fork and bake in the oven for around 15 minutes.
To make the avocado mousse filling, add the avocado, cacao powder and maple syrup to a blender or food processor and blend. Activate the agar agar by heating it with 3 tbsp water in a saucepan and then add to the avocado mousse, blending once again.
Transfer the chocolate mousse filling to the tartlet base and leave to set in the fridge for 2-3 hours.