Heat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with parchment paper, leaving an overhang on the long sides.
Spread the chopped nuts on a baking sheet and toast them for 6 to 8 minutes, until fragrant and lightly golden. Let them cool.
In a large bowl, mash the bananas with a fork until mostly smooth.
Whisk the melted butter and brown sugar into the bananas until combined.
Add the eggs, yogurt and vanilla and whisk until smooth and glossy.
Sprinkle the flour, baking soda, salt and cinnamon over the wet ingredients. Fold with a spatula until just combined, with a few small streaks of flour still showing.
Fold in about three-quarters of the toasted nuts, saving the rest for the top.
Pour the batter into the prepared pan and smooth the top. Scatter the remaining nuts over it, and sprinkle with coarse sugar if you like.
Bake for 55 to 65 minutes, until the top is deep golden and a toothpick inserted in the center comes out with a few moist crumbs. If the top browns too quickly, loosely tent with foil after 40 minutes.
Cool in the pan for 15 minutes, then lift out and cool on a wire rack for at least 15 minutes more before slicing.