Puree the bananas and greek yogurt until smooth and set aside.
Add the all-purpose flour, ground cinnamon, baking soda and salt to a bowl and stir to evenly distribute. Set aside
Add the oil, softened butter, dark brown sugar, vanilla extract and eggs to the bowl of a stand mixer. Beat on medium speed until the mixture is smooth.
Turn the mixer down to low speed and add half of the dry ingredients set aside earlier and half the banana/yogurt mixture. Wait until there are no more dry spots then add the rest of the flour and banana/yogurt mixtures. Continue beating on low speed just until there are no more dry spots.If using a stand mixer make sure to scrape down the sides and bottom of the bowl to get any unincorporated ingredients. Gently fold them into the rest of the batter by hand.
Line a quarter sheet pan with parchment paper and pour the banana cake batter in, spreading with a spatula as needed to make sure it is even.
Bake for 25-30 minutes or until the cake springs back when lightly touched. Let the cake cool completely before topping with the cream cheese frosting and caramel.
Make the Cream Cheese Frosting
Beat the cream cheese and the unsalted butter on high speed in a mixing bowl until completely smooth.
Add the powdered sugar to the mixing bowl and beat again until completely incorporated.
Assemble the Banana Caramel Sheet Cake
Remove the cooled cake from the pan if you plan to transfer it to a display stand or other server.
Spread the cream cheese frosting across the top of the cake using the back of a spoon.
Drizzle the caramel on top of the cream cheese frosting. Add a sprinkle of flaky sea salt here for a salted caramel flavor (this is optional).
Use the back of the spoon again to swirl the caramel gently into the cream cheese frosting. Serve at room temperature.
Refrigerate any leftovers in an airtight container for up to 5 days for optimal taste and texture.
Use a kitchen scale. It's more precise and will give you consistent results
Make sure all the ingredients are at room temperature
You can use a 10-inch square pan instead of a quarter sheet pan. Make sure that the pan is at least 3 inches deep since it will be a little taller than if a larger pan was used.