Preheat oven to 350°F (180°C). Grease a 9-inch (23-cm) round—or heart-shaped—cake pan and either line it with parchment paper or dust bottom and sides of pan with sifted gluten-free cocoa powder.
In double boiler or heatproof bowl set over pot of barely simmering water, melt chocolate, stirring occasionally, until smooth.
In bowl of a food processor, combine chickpeas, eggs and sugar; process until smooth. Add melted chocolate and blend until smooth, stopping occasionally to scrape down sides and make sure chocolate is completely mixed.
Spread batter in prepared cake pan. Bake in preheated oven for 40 minutes, or until a knife inserted into the centre of the cake comes out clean. Cool in pan on a wire rack for 10 to 15 minutes before transferring to a serving plate.