Preheat the oven to 350°F (175°C). Grease and flour a 9-inch (23 cm) round cake pan.
In a large mixing bowl, combine the mashed bananas, plain Greek yoghurt, granulated sugar, eggs, vegetable oil, and vanilla extract. Mix well until smooth.
In a separate bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking soda, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Do not overmix.
Fold in the semi-sweet chocolate chips evenly into the batter.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 10 minutes.
Transfer the cake to a wire rack to cool completely before slicing and serving.