How to Make It
Bring a large saucepan of water to a boil. Fill a large bowl with ice water. Using a sharp paring knife, mark an X on the bottom of each peach. Add the peaches to the saucepan and blanch until the skins start to peel away, 1 to 2 minutes. Transfer the peaches to the ice bath and let cool completely. Peel, halve and pit the peaches and transfer to a large heatproof bowl. Wipe out the saucepan.
In the large saucepan, combine all the remaining ingredients with 1 1/2 cups of water and bring to a boil, stirring to dissolve the sugar. Let the brine cool slightly, then pour over the peaches and let cool completely. Cover and refrigerate overnight.
In a large bowl, whisk 8 cups of water with the sorghum syrup and 2 tablespoons of salt. Add the chicken, cover and refrigerate overnight.
Drain the chicken and wipe out the bowl. Return the chicken to the bowl and toss with 1/2 cup of the olive oil, the vinegar, garlic, chopped herbs and 1 teaspoon of pepper. Let stand at room temperature for 1 hour.
Light a grill and oil the grate. Remove the peaches from the brine and reserve the pickling liquid. Grill the peaches over moderate heat, turning once, until lightly charred, 4 to 5 minutes. Transfer to a work surface. Grill the chicken thighs over moderate heat, turning, until lightly charred and cooked through, 20 to 25 minutes. Transfer to the work surface and let rest for 5 minutes.
In a bowl, toss the arugula with 1 tablespoon of the peach pickling liquid and the remaining 1 tablespoon of olive oil; season with salt and pepper. Arrange the salad, chicken and grilled peaches on a platter and serve.