Prepare charcoal or gas grill to medium-high heat or heat oven to 450 dg.
Using heavy-duty aluminum foil, cut four pieces 2 1/2 ft. long. Fold each piece in half to make a large rectangle. Spray foil pieces generously with cooking spray.
In large bowl stir together cumin, cilantro OR coriander, salt, oil and grated ginger. Rub half of this mixture over chicken and set aside.
Stir lime juice into remaining mixture. Add peaches, sweet potato, pepper and scallions. Toss to coat and evenly place peach mixture on one half of each foil piece. Top each with seaoned chicken.
Create a packet for by folding second half of foil over chicken and vegetables. Tightly seal sides and front edges, leaving space for steam to build.
Place foil packets on grill rack over indirect heat (if gas, burners set medium-high) or place on cookie sheet in oven at 475 dg. Grill or bake 25 minutes. Open packets carefully, making sure sweet potato slices are tender, and transfer contents to 4 serving plates.