Preheat your grill to medium heat or your oven to 400°F (200°C).

Cut four large squares of heavy-duty aluminum foil, approximately 12x12 inches each.

In a medium bowl, whisk together teriyaki sauce, minced garlic, grated ginger, brown sugar, soy sauce, and sesame oil until well combined.

Cut chicken thighs into bite-sized pieces, roughly 1-2 inch chunks for even cooking.

Place equal portions of chicken pieces in the center of each foil square.

Distribute pineapple chunks evenly among the four packets, arranging them around and on top of the chicken.

Pour the teriyaki sauce mixture over each packet, making sure all chicken and pineapple pieces are well coated.

Sprinkle sliced green onions over each packet and season with a pinch of salt and pepper.

Fold the foil by bringing the long sides together and folding them over multiple times to create a tight seal, then fold up the short ends in the same manner.

Place sealed packets on the preheated grill or on a baking sheet in the oven.

Cook for 20-25 minutes on the grill or 25-30 minutes in the oven, until chicken reaches an internal temperature of 165°F.

Carefully open one packet to check doneness, watching out for hot steam.

Once cooked through, carefully open all packets and sprinkle with sesame seeds.

Serve immediately directly from the foil packets or transfer to plates with steamed rice or vegetables.