Heat the grill to 350℉, and set it up for indirect cooking. *For charcoal grilling, use a deflector plate if you have one.
While the grill is heating up, prep the peaches. Use a pastry brush to brush the cut side of each of the peach halves with about 1 teaspoon of honey. Then evenly sprinkle about 1 teaspoon of sugar over each peach half.
Grill the peaches - Place the peach halves cut side down on the grill grates, and grill for about 3-4 minutes, just long enough to get a slight char. You can rotate them 90 degrees halfway through the cooking time to get those beautiful hatch marks, if you wish. The goal is to caramelize and soften, not cook them to mush. Then remove from the grill.
Butter a cast iron skillet by adding 6 tablespoons of melted butter to the bottom of the skillet. Rotate the skillet around so that the melted butter goes up the sides. You should have some melted butter remaining in the bottom of the skillet.
Prepare the cobbler batter - In a large bowl, add 1 cup granulated sugar, 1 cup flour, 1 tablespoon baking powder, and ¼ teaspoon salt. Mix dry ingredients until combined. Then mix together the milk and vanilla extract in a separate bowl. Combine wet and dry ingredients, stirring to blend – but don’t over mix. The batter should be loose (think pancake batter consistency).
Assemble the cobbler - Pour the cobbler batter into the buttered skillet, directly on top of the remaining melted butter. Do not stir the butter into the batter. Nestle the grilled peaches, cut side up, evenly into the wet batter in your skillet.
Cook the cobbler on the grill - Place the skillet on the grill over indirect heat. Close the grill lid and cook at 350°F for about 20 minutes, rotating the skillet if necessary for even baking.
Make the streusel topping - While the cobbler bakes, prepare the streusel topping. In a medium bowl, mix together brown sugar, rolled oats, cinnamon, and salt. Work the cold butter and flour into the mix with a fork until you get a chunky, crumbly texture. Set aside.
Add the streusel to the top of the grilled peach cobbler - After 20 minutes of cooking, sprinkle the streusel evenly over the top of the cobbler. Continue to cook an additional 18-20 minutes.
Remove the cobbler from the grill and allow to cool for about 5-7 minutes. Then serve warm with vanilla ice cream.