Preheat the oven to 180 degrees, line a muffin tin with paper liners and chop the chocolate.
Mix the flour, sugar, baking powder, baking soda, salt and cinnamon in a bowl and set aside.
Mix the egg, oil, yogurt, and vanilla extract. Peel the bananas, mash them with a fork and stir into the egg mixture. Add the flour mixture and stir in briefly. Fold in the chopped chocolate and then pour the batter 2/3 full into the prepared muffin tin.
Bake in the preheated oven for 20-25 minutes until they are golden in color. Take out, let stand briefly in the tin and then leave to cool completely on a wire rack.