Preheat the oven to 350°F (175°C). Prepare brownie batter according to package directions.
Spread batter evenly into a parchment-lined 8x8-inch baking pan.
Bake for 20–25 minutes or until set. Cool completely.
Slice bananas and layer them over the cooled brownies.
In a microwave-safe bowl, heat heavy cream until steaming. Pour over chocolate chips and let sit 1–2 minutes. Stir until smooth.
Pour ganache over the bananas and gently spread. Chill until firm. Slice and enjoy!