Preheat the oven to 350º F. Generously spray a 9x13 pan and set aside.
In a small bowl combine soy milk and apple cider vinegar. Mix together and set aside for 5 minutes to allow the milk to curdle. Once curdled stir in add vanilla extract.
Next, peel and mash your bananas. You can either do this in a bowl with a handheld mixer or potato masher or in a food processor.
In a medium bowl, stir together the flour, baking powder, baking soda, cinnamon, and salt.
Using a stand-up mixer with the paddle attachment or an electric handheld mixer, beat the butter until it's light and airy. Add the brown and white sugar and mix until it's light and fluffy. With the motor running, add the applesauce and mashed bananas scraping down the sides as necessary. The mixture will appear to have separated at this point, but it will come back together once you add the dry ingredients.
Alternating the flour mixture and the buttermilk, add to the mixer in three batches, scraping down the sides as needed, ending with the flour mixture. Mix until it just comes together. Do not over-mix.
Pour batter into the prepared pan and smooth top. Bake until the cake is golden brown (about 35 minututes), and a toothpick comes out clean when inserted in the middle. Remove from the oven and let cool for 60 minutes. Flip out onto wire racks and allow the cake to cool completely. To make the Cream Cheese Frosting, in a stand-up mixer with the paddle attachment, beat together vegan cream cheese and vegan butter until well combined, scraping down the sides as necessary. Add vanilla and combine. With the mixer on its lowest setting, slowly add the powdered sugar one cup at a time, stopping to scrape down the sides between cups. Once all the powdered sugar is added, turn up the speed to medium and mix until smooth and creamy.
Top the cake with a thick layer of cream cheese frosting and serve immediately.