Brush the cooking grates clean. Brush the onion slices with oil. Remove the chicken from the bag and discard the marinade. Season the chicken evenly with the salt and pepper, and then grill over direct medium heat, with the lid closed, until the meat is firm to the touch and no longer pink in the center, 8 to 12 minutes, turning once. At the same time, grill the onions over direct medium heat until tender, 12 to 15 minutes, turning once or twice. Remove from the grill as they are done, and let the chicken rest for 3 to 5 minutes.
Brush the cooking grates clean. Brush the onion slices with oil. Remove the chicken from the bag and discard the marinade. Season the chicken evenly with the salt and pepper, and then grill over direct medium heat, with the lid closed, until an instant-read thermometer inserted into the thickest part of the chicken registers 165°F, 8 to 12 minutes, turning once. At the same time, grill the onions over direct medium heat until tender, 12 to 15 minutes, turning once or twice. Remove from the grill as they are done, and let the chicken rest for 3 to 5 minutes.
Brush the cooking grates clean. Brush the onion slices with oil. Remove the chicken from the bag and discard the marinade. Season the chicken evenly with the salt and pepper, and then grill over medium heat, with the lid closed, until the thickest part of the chicken registers 165°F, 8 to 12 minutes, turning once. At the same time, grill the onions over medium heat until tender, 12 to 15 minutes, turning once or twice. Remove from the grill as they are done, and let the chicken rest for 3 to 5 minutes.