Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with parchment for easy removal.

In a bowl, whisk together the flour, baking soda, salt, and 1 teaspoon ground cinnamon.

In a separate large bowl, whisk the melted butter and granulated sugar until glossy. Add the eggs one at a time, whisking until smooth, then stir in vanilla.

Mash the bananas until mostly smooth with a few small chunks for texture. Stir the mashed banana and yogurt into the wet mixture until combined.

Fold the dry ingredients into the wet mixture gently, just until no streaks of flour remain. If using nuts or chocolate chips, fold them in here.

In a small bowl, mix the brown sugar and 1 tablespoon cinnamon for the swirl.

Pour half of the batter into the prepared pan, smoothing the top. Sprinkle half of the cinnamon-sugar mixture evenly over the batter.

Add the remaining batter, then sprinkle the rest of the cinnamon-sugar on top.

Use a butter knife to gently swirl the layers.

Bake for 55 to 65 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs.

Let the loaf cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.