Preheat the oven to 350 degrees F. Spray an 8x4-inch loaf pan with nonstick spray.
In a medium bowl, whisk together the flour, baking soda & salt.
In a separate large bowl, use an electric mixer to combine the sugar and butter at medium speed until well blended. Add the eggs, one at a time, beating well after each addition. Add the banana, yogurt and vanilla; beat until blended. Add the flour mixture; beat at low speed just until the flour is incorporated (don’t over mix).
Spoon the Nutella into a medium bowl and soften in the microwave for about 10 seconds. Add 1 cup of the banana bread batter to the Nutella and stir until blended well. Spoon the Nutella batter alternately with the plain banana bread batter into the prepared pan. Swirl the batters together gently with a knife.
Bake 60 to 70 minutes, or until a toothpick inserted into the center comes out clean. Check the oven at 45 minutes to check the top of the bread for browning. If it’s browning too quickly, cover lightly with foil for the remainder of the baking. Cool for at least 15 minutes in the pan, and then turn out onto a wire rack to cool completely.