Preheat the oven to 375F degrees (190C or 180C fan forced). Line a 12 cavity muffin pan with muffin papers, or spray with non-stick cooking spray and flour. You'll end up with about 12-14 muffins total, so you may need 2 tins.
In a medium bowl whisk together the flour, cocoa, baking powder, baking soda and salt. Set aside.
In a separate large bowl, whisk together the oil, brown sugar, granulated sugar, eggs and vanilla extract.
Whisk the mashed bananas and yogurt into the oil mixture.
Gently fold the dry ingredients into the wet ingredients using a rubber spatula or wooden spoon. Be careful not to over mix.
When the ingredients look about 90% combined, gently fold in the chocolate chips.
Spoon about ¼ - ⅓ cup of muffin batter into the cavities of your prepared muffin pan. You'll end up with 12-14 muffins total.
Bake in the preheated oven for about 20-24 minutes, or until an inserted toothpick comes out clean or with a melted chocolate chip or a few moist muffin crumbs.
Let to cool in the pan for 10 minutes, then remove and continue cooling on a wire rack.