Preheat the grill to medium-high heat or the oven to 400°F (200°C).
In a mixing bowl, combine the teriyaki sauce, sesame oil, and a pinch of salt and pepper.
Add the chicken thighs to the bowl and coat them well in the marinade. Let them marinate for about 10 minutes while you prepare the other ingredients.
Tear four sheets of aluminum foil, each large enough to create a packet (about 12x12 inches).
Place one marinated chicken thigh in the center of each foil sheet.
Divide the diced pineapple and sliced bell peppers evenly among the packets, placing them around the chicken.
Sprinkle chopped green onions on top of each packet.
Fold the sides of the foil over the chicken and vegetables, sealing them tightly to create packets.
Place the foil packets on the grill and cook for about 25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C). If using the oven, place the packets on a baking sheet and cook for the same amount of time.
Carefully remove the packets from the grill or oven. Let them sit for a few minutes before opening.
Serve the contents of the packets over cooked rice or quinoa, if desired.