Rinse the pork chops, pat dry and place in a large sealable food bag.
Bring the apple cider, water, 1/2 cup sugar and 1/3 cup sea salt to a boil in a small saucepan. Stir until sugar and salt dissolves. Remove from heat and add a few ice cubes to cool the brine. Allow to cool completely then add to the bags with the pork chops along with the rosemary sprigs, garlic cloves and black peppercorns. Refrigerate for at least 4 hours up to overnight.
Remove the pork chops from the brine and discard the brine. Pat the pork dry with a paper towel and lightly brush with olive oil and season with kosher salt and freshly ground black pepper.
Preheat one side of the BBQ grill to high and one side to low. Brown the chops for about 5 minutes or until nice grill marks develop and then turn to the other side and cook for another 5 minutes. Turn the chops over and move them to the low-heat part of the grill. Cook for another 10-12 minutes or until cooked to your liking. Transfer to a platter and tent with aluminium foil for about 5 minutes.
While pork chops are cooking on the low temperature side of the grill, lightly coat the peach halves on the fleshy side of the fruit with 1 tablespoon of olive oil and sprinkle with 2 teaspoons of the sugar.
Grill the peaches flesh side down on the high temperature side of the grill for about 4-5 minutes on each side. Transfer to a cutting board and cut into slices. Mix the red onions with the remaining tablespoon of olive oil, white balsamic vinegar, sriracha sauce, 1 teaspoon sugar and a pinch of kosher salt. Add the sliced peaches to the red onions and gently mix.
Top the pork chops with the peaches and onion mix and garnish with torn basil leaves.