Preheat oven to 425°F (220°C). Line a 12-cup muffin tin with liners or grease well.
In a medium bowl, whisk together the flour, baking powder, salt, and cinnamon.
In a large bowl, mash the bananas until mostly smooth with a few small lumps.
Whisk the coconut sugar, melted coconut oil, eggs, vanilla, and yogurt into the mashed banana until combined.
Add the dry ingredients to the wet ingredients and fold together with a spatula until just combined; a few streaks of flour are fine. Do not overmix!
Fold in the chopped nuts & chocolate gently.
Divide the batter evenly among the muffin cups, filling each to the top. Sprinkle extra chopped nuts over each one if preferred.
Bake at 425°F for 5 minutes, then, without opening the oven, lower the temperature to 350°F (175°C) and bake for another 14–16 minutes, until a toothpick comes out clean.
Cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.