Preheat oven to 350℉. Line a small 6 inch round cake pan with parchment paper.
In a large bowl, add in your bananas, Greek yogurt, eggs, tapioca, salt and mix together until incorporated. Transfer batter to cake pan and spread out evenly. Bake for 1 hour or until toothpick comes out clean. Transfer to wire rack and let cool completely.
In a small pan over medium heat, add in coconut oil, maple syrup, peanut butter, salt and mix together until combined and smooth - a few minutes. Please note that the sauce will be drippy at first but once you take it off the heat, give it 15-20 minutes to thicken up and resemble a more caramel texture.
