Preheat a grill or grill pan over medium-high. In a baking dish, soak eight 10-inch wooden skewers in water, 30 minutes.
On a skewer, thread 1 piece each zucchini, yellow squash, eggplant, red onion, basil and steak; repeat once more. Repeat layering with the remaining skewers, creating 8 kebabs.
Tear off eight 12-by-12-inch sheets of aluminum foil. Stack two sheets of foil and fold up the edges to make a bowl; repeat with the remaining foil. Divide the rice, stock, butter and chopped onion among the foil bowls; season. Fold the edges of the foil together and crimp to seal, creating 4 packets.
Brush the kebabs with the oil; season. Grill the kebabs and rice packets, turning the kebabs occasionally, until the vegetables start to char, about 10 minutes. Cover and cook until the vegetables are tender, the liquid in the packets is absorbed and the rice is tender, about 10 minutes more. Serve the kebabs with the rice packets.