Topping: Combine ingredients except the buttermilk. Using a pastry cutter, combine mixture until fine. Slowly add in the buttermilk and stir to incorporate. Set aside.
Filling: In a medium mixing bowl, combine all ingredients excluding the peaches. Once combined, carefully fold in the peaches.
Grease a 12 inch cast iron skillet and pour peach mixture evenly onto the bottom.
Drop batter evenly on top of peaches.
Place cast iron skillet onto grill/smoker over indirect heat and allow to bake for about 45-50 minutes, or until golden brown.