Put the coconut milk in the fridge and chill overnight.
Melt the chocolate in a bowl over hot water or in the microwave. Leave to cool slightly.
Drain the chickpeas and put the liquid into the bowl of a free-standing mixer. Whisk until it forms soft peaks. Add the melted chocolate, agave, vodka and coffee liqueur and stir gently to combine. Divide between 6 martini glasses. Chill in the fridge for a couple of hours, or until set.
Drain the liquid from the coconut milk and put the solids in the bowl of a free-standing mixer. Whisk until it has the consistency of whipped cream. Decorate the top of the mousses with the cream. Dust with cocoa powder, if desired.