Preheat the grill for high heat. Lightly grease 4 large sheets of heavy duty aluminum foil.
Stuff each mushroom with equal amounts of green onions and pine nuts. Place 6 mushrooms on each piece of aluminum foil. Drizzle with olive oil, and season with salt and pepper. Seal the foil around the mushrooms, forming 4 packets.
Place the foil packets on the preheated grill, and cook 20 minutes, until mushrooms are tender.