Preheat grill to medium-high heat (approximately 400°F / 205°C).
In a medium bowl, combine chicken cubes with 0.5 cup of BBQ sauce and toss to coat evenly.
In a large bowl, toss the zucchinis, bell peppers, and red onion with olive oil, garlic powder, salt, and black pepper.
Cut four 12x18 inch sheets of heavy-duty aluminum foil and lay them flat on a work surface.
Divide the vegetable mixture evenly among the center of the four foil sheets.
Top the vegetables with the marinated chicken cubes.
Drizzle the remaining 0.5 cup of BBQ sauce over the chicken in each packet.
Fold the sides of the foil over the contents and seal the edges tightly to create a secure pouch, leaving a small amount of space for steam to circulate.
Place the foil packs on the grill and cook for 15 to 20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Carefully open the packets to release steam before serving.