In a medium sized bowl, combine chicken thighs with reserved 1/2 of balsamic vinigeratte. Season with additional 1/2 teaspoon of kosher salt and 1/4 teaspoon black pepper. Cover and let marinate between 30 minutes and 2 hours before grilling. While chicken is marinating, prepare croutons and crispy prosciutto.
Whisk together barbecue sauce and apricot preserves and divide. Serve 1/2 of sauce alongside salad for additional topping and use 1/2 for brushing chicken at the end of grilling.
Remove chicken from marinade, letting excess marinade fall off before placing on medium-high grill. For best results and texture, grill chicken thighs to an internal temperature between 175℉ and 195℉. Brush chicken with barbecue sauce only during the last minute or two of grilling. This will allow the barbecue sauce to caramelize without burning. Let chicken rest and slice before adding to salad. Chicken and peaches can be served at room temperature or chilled on salad.
Instead of trying to remove the pit from the peaches, which can be messy, cut the peach around the pit by slicing the the two rounded sides (the cheeks) off the peach. Then cut the remaining sides off. Brush all cut sides with olive oil and season lightly with salt and pepper. Grill over medium heat 3-5 minutes, or until grill marks form and peach have started to become tender. After grilling, cut peaches into smaller slices.