Place the chicken in a bowl or sturdy resealable plastic bag.
Make the marinade: In a separate bowl, combine the soy sauce, sugar, ginger, garlic, rice wine, sesame oil, rice vinegar, and five-spice powder, if using. Whisk until the sugar crystals dissolve. Pour over the chicken, ensuring every piece is coated with the marinade. Cover the bowl (or seal the bag) and refrigerate the chicken for 4 to 6 hours.
Assemble the foil packets: Tear off 8 10-inch pieces of Reynolds Wrap® Non-Stick Aluminum Foil. Arrange one piece on a flat surface with the long side parallel to you, dull side up so the chicken lifts right off after cooking. Lift two pieces of chicken out of the marinade and arrange in the center of the foil, overlapping slightly.
Top with 1 teaspoon of the marinade. Bring the long edges of the foil together. Fold twice. Next, fold the short edges twice to completely enclose the chicken. Repeat for the remaining packets. You should have 8 total. Transfer to a rimmed sheet pan (this makes transporting to and from the grill easier).
In the meantime, set up your grill for direct grilling and preheat to medium-high (400°F).
Arrange the packets, starting with the seam sides up, on the grill grate. (Work in batches if your grill grate is not large enough to accommodate all eight at once.) Grill for 4 to 5 minutes per side, turning with tongs, until the chicken is cooked through. The packets may puff with steam as they cook. Carefully open a packet to check for doneness, avoiding any escaping steam. Using tongs, transfer the hot packets to the rimmed sheet pan.
Carefully open the remaining packets. Scatter scallions on top of the chicken and sprinkle with sesame seeds. Serve directly from the Reynolds Wrap® Non-Stick Aluminum Foil packets.