Heat oven to 350°F (175°C) and grease a 9x5-inch loaf pan. Whisk together the mashed bananas, melted butter, sugar, eggs, vanilla, and yogurt until smooth.

Sprinkle the flour, baking soda, and salt over the wet mixture. Fold gently just until no dry streaks remain.

Warm the Nutella until drizzly. Pour half the batter into the pan, dollop half the Nutella, and swirl with a butter knife. Repeat with remaining batter and Nutella, swirling lightly.

Bake for 55 to 65 minutes, until a toothpick comes out with moist crumbs. Tent with foil if the top browns too quickly after 40 minutes.

Cool in the pan for 10 minutes, then turn out onto a rack to cool completely before slicing.