Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease the springform pan (26 cm Ø). Drain the mango for the dough. Place in a blender with walnuts, eggs, sugar and orange peel.
Mix flour, cocoa, cinnamon and baking powder. Pour into the mixer. Mix at intervals to a smooth dough, stopping the mixer at intervals to release the dough from the rim of the bowl.
Pour the dough into the mould and smooth it down. Bake in a hot oven for about 35 minutes (chopstick test). Take out and let cool down. Remove from the tin and let it cool down on a cake rack.
Melt the chocolate coating in a hot water bath. Spread all around the cake. Let it dry.