Heat the oven to 170°C fan and line a loaf tin with baking paper.
Mix the rice flour, ground almonds, baking powder, baking soda and salt in a bowl. Set aside
Peel the bananas, and in a large bowl, big enough to take all the ingredients later, mash the peeled bananas thoroughly. Beat in the vanilla, then the yogurt and, one by one, the eggs followed by the melted and cooled coconut oil and sugar.
Gradually add the flour to the wet mixture. Scrape down the sides of the bowl to make sure all is combined, and then fold in the chopped chocolate and walnuts.
Pour the batter into the lined loaf tin - it will come close to the top. Bake it in the oven for 50-55 minutes until shrinking from the sides of the tin and a toothpick inserted in the middle comes out cleanish (if you manage to avoid the melted chocolate) with a few damp crumbs sticking to it. Sit the tin on a wire rack, and allow the cake to cool completely before removing from the tin.