Preheat the oven to 350°F (175°C). Spray a 9x5-inch loaf pan with cooking spray and line the bottom and two sides with a piece of parchment.

Make the filling: In a small bowl, whisk together the brown sugar, cocoa powder, and cinnamon. Set aside.

Make the chocolate streusel: In a medium bowl, combine the sugar, flour, cocoa powder, cinnamon, and salt. Add the melted butter and mix using clean hands until small, irregular clumps the size of marbles form. Set aside.

Mash the bananas and add the butter: To make the banana bread cake, mash the ripe bananas with a fork until completely smooth in a large mixing bowl. Stir the melted butter into the mashed bananas.

Mix in the remaining ingredients: Mix in the baking soda and salt. Stir in the sugar, beaten egg, and vanilla extract. Mix in the flour and cinnamon until a smooth batter forms. Add the chocolate chips and stir until evenly distributed throughout the batter.

Add everything to the loaf pan: Pour half of the cake batter into the prepared loaf pan and spread into an even layer. Sprinkle the filling mixture on top of the batter in an even layer and top with the remaining cake batter. Sprinkle the top of the cake with the chocolate streusel, pressing it in slightly so it sticks.

Bake: Bake until a toothpick or wooden skewer inserted into the center comes out clean, 60 to 70 minutes. A few dry crumbs are okay but wet batter is not. If you hit a melted chocolate chip, test in a different spot.

Cool and serve: Remove from oven and let cool in the pan for 10 minutes. Then remove the banana bread from the pan and let cool completely on a wire rack. Wrapped tightly, the banana bread cake will keep at room temperature for 4 days. For longer storage, refrigerate the loaf up to 5 days or freeze it. Love the recipe? Leave us stars and a comment below!