Preheat the oven to 350°F. Grease and line an 8 or 9-inch round cake pan with parchment paper.
In a large bowl, whisk together banana, eggs, Greek yogurt, coconut sugar, vanilla extract, and apple cider vinegar until smooth.
Slowly whisk in the melted coconut oil.
Stir in the milk.
In a separate bowl, whisk together gluten-free flour, baking powder, baking soda, cinnamon, and sea salt.
Add the dry ingredients to the wet ingredients and stir until just combined. The batter should be thick but easily spreadable. Avoid overmixing.
Transfer batter to the prepared pan and smooth the top.
Bake for 26–30 minutes, checking around the 24-minute mark. The cake is done when the center springs back lightly and a toothpick inserted into the center comes out clean or with a few moist crumbs attached. Allow the cake to cool in the pan for 10–15 minutes before transferring to a wire rack to cool completely.
Chill before frosting (option to make my Healthy Chocolate Date Frosting recipe), if desired. Enjoy!