Melt the chocolate in the microwave or over low heat. Note: I always recommend to stop heating when half the chocolate is melted and continue stirring away from the heat source to melt the remaining chocolate without burning it.
Add agave syrup to the chocolate if you like it sweeter.
Let cool the chocolate for 15 minutes. Note: make sure to wait the recommended amount of time.
In the meantime, drain the chickpeas and collect the juice. Weigh 120g of aquafaba and add it to a large mixing bowl. Whip it with an electric hand mixer for AT LEAST 7 minutes (this is very important!). I recommend setting a timer.
When the chocolate has cooled down, transfer it to a large bowl.
Gently fold the foamed aquafaba into the melted chocolate (just like you would incorporate whipped egg whites into cake batter).
With a teaspoon, fill the mousse into a silicon ice cube tray. Let sit in the fridge for at least 4 hours or overnight. This allows the mousse to firm up.