Preheat the oven to 350°F/175°C (320°F/160°C for dark metal loaf pans) and line your loaf pan with parchment paper.
In a bowl, sift together flour, cocoa powder, salt, and baking soda. Set aside.
In a large bowl, cream together the softened unsalted butter and granulated sugar. Once it's pale and fluffy, beat in the egg. Stir in the mashed banana, yogurt, milk, and vanilla.
Add the dry ingredients into the wet ingredients, leaving a little in the bowl (about ¼ cup of the dry ingredients). Toss the chocolate chips in the bowl so each chocolate chip is covered with flour.
Pour the batter into the prepared loaf pan and bake in the preheated oven for about 1 hour and 15 minutes. Let it cool completely before slicing.