Prepare boiling water in a pan. No need to measure yet.
Preheat oven to 180 °C. Lightly grease a loaf pan - 81/2 X 3 inch.
Mash the bananas in a large bowl, until relatively smooth. Spoon the mashed bananas into the measuring cup to measure and then return to mixing bowl.
Beat in the brown sugar, oil, milk and vanilla.
Add wheat flour, baking soda, cinnamon and salt. Mix gently. It is ok if some flour is visible. Do not overmix.
Transfer 1 cup batter in a separate bowl. In a small cup, mix cocoa powder with 3 Tbsp boiling water and stir vigorously to achieve smooth consistency. Mix chocolate mixture into the separate 1 cup batter and mix well to incorporate.
Add 3 tbsp of boiling water to vanilla batter and mix till relatively smooth.
Alternately scoop vanilla and chocolate batter with an ice-cream scoop or 1/2 cup into the prepared pan. Play with whatever pattern you wish to create. Once all the batter is in, just give quick nice swirl with a fork/ toothpick or knife.
Bake for 52-55 mins. Allow to cool in tin for 10 mins and then remove. Eat fresh with milk or for kids as snack.