Preheat your oven to 350ºF (175ºC) and prepare your muffin cups by lining them with paper liners or spraying them with cooking spray.

In a large mixing bowl, mash about three overripe bananas until smooth, then stir in melted butter, eggs, Greek yogurt, and vanilla extract.

In a separate bowl, sift together flour, baking soda, sugar, and salt. Whisk until well combined.

Gently fold the dry ingredients into the wet mixture until just combined.

Divide the batter evenly among the muffin cups, filling each about two-thirds full.

Microwave Nutella for about 20 seconds to soften it, drizzle over the batter, and swirl it in with a knife.

Bake for 15-20 minutes for regular-sized muffins or 20-25 minutes for giant muffins, until a toothpick comes out clean.

Let the muffins cool in the pan for about 15 minutes before transferring them to a wire rack.