Grill the peaches at medium-low heat on your Bull Grill. Because of the sugar in the peaches they will caramelize quickly and become sticky. Remove them from heat as soon as they get grill marks.
Peel the skin from the peaches if desired. I left the skin on mine.
Combine the peaches, simple syrup, lime juice and mint in a blender and blend until smooth. Put the mixture into the fridge to chill for 30-60 minutes.
Fill glasses half way with Prosecco and then the remainder with grill peach mixture.
Garnish with mint and grilled peach slices.