1Combine Greek yogurt, frozen bananas, and sugar in a blender; blend until smooth.
2Pour yogurt mixture into an ice cream maker. Freeze according to manufacturer's instructions until yogurt is the texture of soft-serve ice cream, about 15 minutes. Stir in walnuts and chocolate chips.
When bananas are too ripe to eat, peel them and keep in a freezer bag for smoothies and ice cream.
As an alternative, mix walnuts and chocolate chips into the yogurt mixture after blending and put directly into the freezer.