Line a 9×13 inch baking pan with parchment paper, making sure you have some overhang on the sides – this will make it much easier to lift out later. Give the paper a light spray with cooking spray to prevent sticking.
In a large bowl, combine the Greek yogurt, honey, and a tiny pinch of salt.
Peel and mash your bananas with a fork until they’re pretty smooth. You want them about the consistency of baby food.
Fold the mashed bananas into your yogurt mixture until well combined. The mixture might look a bit loose – that’s totally normal.
Pour the mixture into your prepared pan, using a spatula to spread it into an even layer about 1/4 inch thick. Give the pan a few gentle taps on the counter to get rid of any air bubbles.
Warm your Nutella in the microwave for about 20 seconds. Drop spoonfuls of the warm Nutella all over the yogurt mixture, then use a butter knife to create pretty swirls.
Sprinkle the chopped hazelnuts and mini chocolate chips evenly over the top. Press them in very gently with the palm of your hand so they stick when frozen.
Place the pan in the freezer and let it freeze until completely solid, at least 4 hours but preferably overnight. You’ll know it’s ready when the surface is firm to the touch and no longer gives when pressed.
When frozen solid, lift the bark out using the parchment paper overhang and place on a cutting board. Let it sit for about 2 minutes to soften before you cut it.
Using a sharp knife, cut or break the bark into irregular pieces. If the bark is too hard to cut, wait another minute or two.