Peel and freeze the bananas ahead of time. This isn't entirely necessary, but it helps speed things along.
Combine all ingredients except the hazelnuts and chocolate chips in a blender and process until smooth. Chill mixture for 30 minutes to 1 hour, until it reaches about 40 degrees.
While the yogurt mixture is in the fridge, toast the hazelnuts. Preheat the oven to 350 F. Spread the nuts in a single layer on a baking sheet. Toast until just beginning to be fragrant, about 3 to 5 minutes.
Transfer yogurt mixture to an ice cream maker and churn according to package directions. During the last 5 minutes or so, add in the hazelnut pieces and chocolate chips.