Preheat grill to medium-high heat.
In a large bowl, combine the sausages, bell peppers, zucchini, and red onion. Drizzle with olive oil, then add garlic powder, Italian seasoning, salt, and pepper. Toss to combine.
Cut four large sheets of aluminum foil. Divide the sausage and vegetable mixture among the sheets. Fold the foil over the mixture and crimp the edges to seal, creating packets.
Place the foil packets on the grill. Close the grill lid and cook for about 20-25 minutes, until the sausages are cooked through and the vegetables are tender.
Carefully open the foil packets and serve hot.