Prepare all the ingredients: Mash 4 bananas with a fork. Roughly chop the nuts and chocolate. In a small pot melt the butter, take it off the heat and let it cool.
In a small bowl, mix the flour, salt, spices, baking powder, and baking soda together. Set aside.
Prepare a 9x5 inch loaf pan (23x13 cm) or 10x4.5 inch (25.5x11.5cm) by buttering it and lining it with parchment paper.
Preheat the oven to 325 °F / 160 °C / Gas Mark 3, no fan.
Place the eggs and sugar in a mixing bowl, whisk with a mixer fitted with a whisk attachment on medium-high speed for 5 minutes until the mixture is pale, light and foamy.
Add the mashed bananas and melted and cooled butter, mix until just combined.
Sieve the flour mixture into the batter, stir in with a spatula, until partially combined.
Add the chopped chocolate and walnuts, fold in, taking care, not to over mix the batter.
Pour the batter into the prepared loaf pan.
Lay the banana slices (the reserved ½ banana) on top.
Bake for 55 minutes, or until a cake tester/bamboo skewer comes out clean. It may run longer or shorter in your oven.