Preheat the oven to 350 degrees F. Lightly brush the inside of a 10-by-5-inch loaf pan with coconut oil and line with a strip of parchment paper. Set aside.
Mash the bananas with the back of a fork in a large bowl until only a few lumps remain. Add the eggs and mix until smooth. Using the fork, whisk in the coconut oil, yogurt, sugar, salt and vanilla until smooth and incorporated. Add the flour and baking soda and use a rubber spatula to stir until combined, being careful not to overmix. Fold in the hazelnuts, if using, and the chocolate chips.
Pour half of the batter into the prepared pan. Dollop half of the hazelnut spread over the top of the batter. Swirl the spread into the batter using the tip of a knife. Top with the remaining batter and repeat with the remaining hazelnut spread. Bake until the bread is firm to the touch and a toothpick inserted in the center comes out with very few crumbs (the streaks of hazelnut spread will still be wet), 1 hour to 1 hour and 5 minutes. Allow to cool for 30 minutes in the pan.
Turn the pan on its side and let rest an additional 30 minutes. Loosen the edges with a knife and remove to a wire rack to cool completely. The bread will keep for 4 days at room temperature.