For the oven, preheat to 425°F. For grilling, heat your grill to a medium-high setting of 450°F.
Prepare five large sheets of heavy-duty foil, each approximately 12 x 18 inches. Generously spray each sheet with nonstick cooking spray.
In a large mixing bowl, combine all ingredients except the butter. Mix thoroughly to coat everything evenly.
Divide the mixture evenly among the five sheets, placing each portion in the center. Add 1 tablespoon of butter to the top of each pile of ingredients.
To secure the packets, fold the shorter sides together at the top and roll down, leaving a bit of space for steam to circulate. Then, tightly roll up the ends to fully seal each packet.
Place the foil packets on the grill, cooking for about 25–30 minutes, turning each packet halfway through. Alternatively, bake the packets in the oven for 30–35 minutes, or until the vegetables reach desired tenderness.
To avoid losing steam, test only one packet by opening it slightly; each release of steam can extend the cooking time.
Serve the packets immediately, allowing everyone to enjoy their flavorful meal straight from the foil.