Preheat oven to 350F. Lightly grease a 9x13 baking pan. Set aside.

In a large bowl, beat mashed banana, sugar, yogurt, oil, eggs, milk, and vanilla until smooth. In a separate bowl, combine flour, cocoa, baking powder, baking soda, and salt. Fold flour mixture into liquid until just combined. Fold in chocolate chips.

Scrape batter into prepared pan and bake at 350F 40-45 minutes until a toothpick inserted in middle comes out with moist crumbs sticking to it. Cool cake on a wire cooling rack, then slice into squares. Enjoy!