Preheat the oven to 180°C.
Put sugar and eggs in a mixer bowl and mix until well incorporated.
Add mashed up bananas and mix again.
Add yogurt and mix again until just incorporated.
Add flour, baking powder, bicarbonate of soda, cinnamon and mixed spice and mix well until combined. Towards the end add in melted butter and mix some more.
Add some walnut pieces (if using) and fold in gently until combined.
Pour the mixture into tin loaf (roughly 23 x 11cm) lightly greased and sprinkled with flour.
Bake until toothpick or skewer inserted into centre comes out clean approx 55min.
Let it rest in a tin for a few minutes before turning out onto a cooling rack.
Drizzle with melted chocolate if you wish.