Prepare the Vegetables
One of the most important steps when learning how to grill vegetables in aluminum foil is preparing them properly before the grilling even occurs. First, you must select, clean and season the vegetables. Determine what vegetables you will use. Popular choices for use on the grill include potatoes, pepper, corn, or tomatoes, though you can experiment with nearly anything. Wash the vegetables thoroughly, and peel if necessary. At this point, it is also important to cut them into even, uniform pieces in order to encourage even cooking. Place the prepared vegetables into a large bowl, and toss with olive oil, butter, or a non-stick cooking spray. Season the vegetables with salt, pepper, garlic, ginger, or other seasonings of your choice. Make sure all of the vegetables are evenly coated with seasoning.
Prepare the Aluminum Foil
Unroll a large piece of aluminum foil, and place it on a flat surface such as a countertop or table. Spray the aluminum foil with a non-stick cooking spray or coat with butter, and spread the prepared vegetables over the aluminum foil. Unroll another piece of foil that is approximately the same size, and use it to cover the vegetables. Starting at one end, begin rolling the two pieces of foil onto themselves. Continue this as you work your way around the entire piece of aluminum foil, ending where you started. This will create a secure "pouch," which will be perfect for steaming.
Grill the Vegetables
Turn on the grill, and gradually increase the temperature to a normal level. Once the grill has reached an ideal temperature, carefully place the vegetables onto the rack. Be aware that vegetables are more dense than meats, and can take up to 20 minutes to cook thoroughly. If you are also cooking chicken, beef, or fish, keep this time requirement in mind, and put the meats on the grill when appropriate. After about 20 minutes of cooking, use a pair of barbeque tongs to carefully open one end of the foil cooking packet. Test one of the vegetables with a metal fork. If the fork is easily inserted into the vegetables, then they have been cooked properly. If it is difficult to get the fork into the vegetable, then cook them for a few more minutes. Continue testing the vegetables regularly for doneness.
Serve the Vegetables
Carefully remove the aluminum foil packet from the grill using barbeque tongs. Set the packet on a cutting board or other surface that can handle heat, and let cool for a few minutes until the foil is touchable. Once you can handle the foil, carefully loosen one end of the packet, and pour the vegetables onto a serving platter. Serve with burgers, chicken, or fish, and enjoy. These vegetables taste so great that your guests will be asking for advise on how to grill vegetables in aluminum foil.