Preheat oven to 350 degrees.
Line a 9 x 5 metal loaf pan with parchment paper then set aside.
In a large bowl, combine flour, baking soda, salt and brown sugar. Set aside.
In a separate mixing bowl, whisk mashed bananas and beaten eggs with vanilla and Greek yogurt until combined.
Add cooled melted butter to the mashed banana mixture. Stir to combine.
Add flour mixture, 1 cup at a time then gently stir until incorporated. Scrape down the sides of the bowl with a rubber spatula as needed. Avoid overmixing.
Spoon 1 cup of banana bread batter into the parchment lined loaf pan.
Microwave Nutella in a heatsafe bowl for 10 seconds then stir until smooth.
Dollop 3 Tablespoons of Nutella on top of the banana batter layer in the loaf pan.
Top with 1 cup of banana bread batter.
Dollop 3 Tablespoons of Nutella onto the banana batter layer.
Top with remaining banana bread batter.
Spoon remaining Nutella onto the banana batter.
Using a knife, swirl banana bread batter and Nutella together in the loaf pan to create a marbling effect.
Bake for 60 minutes or until a toothpick inserted into the center of the loaf comes out clean. Tent bread with foil while it bakes if it appears to be overbrowning.
Cool bread in the pan for 10 minutes before turning loaf out onto a rack to cool completely.
Slice and serve.
Bread can be stored in an airtight container at room temperature up to 2 days or in the refrigerator up to 7 days.