Prepare the Bananas: Preheat the oven to 350°F. Grease a 9 x 5-inch loaf pan and line it with parchment paper if desired. Peel the ripe bananas and place them in a large mixing bowl. Mash them with a fork until mostly smooth, leaving a few small pieces for extra banana texture.
Step 2: Combine the Wet Ingredients: Add the melted butter, granulated sugar, brown sugar, eggs, and vanilla extract to the mashed bananas. Whisk until the mixture is smooth and well combined.
Combine the Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, salt, and optional espresso powder. Mix until the cocoa powder is evenly distributed and there are no noticeable lumps.
Make the Batter: Gradually add the dry ingredients to the banana mixture. Using a rubber spatula, gently fold everything together just until no visible streaks of flour remain. Avoid overmixing, as this can make the finished banana bread dense.
Add the Chocolate: Fold the semisweet chocolate chips and chocolate chunks into the batter. Reserve a small handful of chocolate chips or chunks for sprinkling over the top before baking.
Fill the Loaf Pan: Pour the chocolate banana bread batter into the prepared loaf pan. Smooth the top with a spatula, then sprinkle the reserved chocolate chips and chunks evenly over the surface.
Bake Until Done: Place the loaf pan in the preheated oven and bake for 50–60 minutes. The bread is ready when a toothpick inserted into the center comes out with a few moist crumbs attached. Melted chocolate on the toothpick is fine, but there should be no wet batter.
Cool and Slice: Remove the banana bread from the oven and let it cool in the pan for 10–15 minutes. Transfer it to a wire rack and allow it to cool further before slicing. Serve slightly warm for soft, melty chocolate throughout each slice.