Step 1: Preheat your oven to 350°F (175°C).
Step 2: Grease a 9x13 inch baking pan or line it with parchment paper.
Step 3: In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
Step 4: In a large mixing bowl, beat the butter and sugar together until light and fluffy for about 3-4 minutes.
Step 5: Add in the eggs, Greek yogurt, and vanilla extract. Beat until well combined.
Step 6: Stir in the mashed bananas until fully integrated.
Step 7: Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Step 8: Spoon half of the batter into the prepared pan, drizzle half of the Nutella, and create swirls.
Step 9: Bake for 30-35 minutes or until a toothpick comes out clean.
Step 10: Let the cake cool in the pan for about 10 minutes, then transfer to a cooling rack.
Step 11: For the frosting, beat the butter until creamy, add Nutella, and mix in powdered sugar until smooth.
Step 12: Once the cake is cool, spread the Nutella frosting over the top.