Toss peach pieces together with oil and sugar until well coated. Arrange pieces on a rimmed parchment lined baking sheet cut sides facing up and roast until fruit is fragrant, shirveled and sightly darkened, about 30 minutes.
Remove half of the peach pieces to the blender and half of the greek yogurt along with half of the ice cream and process to a smooth uniform consistency.
Note this recipe makes 4 extremely large servings and i assume that a standard blender will not be able to accommodate the entire batch.
You may choose to blend everything together if you do have a blender with a large enough bowl.
Pour into 2 large glasses and repeat with remaining ingredients. Serve immediately.