The George Foreman grill works as a contact grill. This means that the machine's hot metal parts grill the food from both sides, much like a sandwich toaster. Vegetables can be cooked in the George Foreman machine. However, as Andrea Chesman points out in "The New Vegetarian Grill," the device often applies too much heat around the vegetables, causing them to steam cook. Remove any excess moisture and cook the vegetables quickly to get the best possible grilled flavor from your George Foreman machine. Different vegetables also cook at different times.
Prepare your vegetables. Cut vegetables such as zucchini, eggplant or carrot into thick slices at least 1/2 inch thick. Break cauliflower and broccoli into small pieces around 1 inch thick. The size of the vegetable slices is important. If you slice the vegetables too thinly, they may not touch both sides of the grill when it is closed; too thick and the vegetables won't cook properly in the middle.
Rinse each piece of vegetable with water and blot them totally dry on a piece of kitchen towel. Absorb as much moisture as you can, particularly with watery vegetables such as zucchini.
Use a basting brush to cover the vegetables in a very thin layer of olive oil. Sprinkle on as much pepper and salt as you prefer.
Turn on the George Foreman grill and allow it to heat up fully. Open the top to make it easy to insert the vegetables.
Space the vegetables in a single layer on the grill. Don't stack the vegetables or they won't cook evenly.
Grill the vegetables for four to six minutes, depending on the thickness and type of vegetable. For example, according to the authors of "George Foreman's Indoor Grilling Made Easy," you should grill cabbage for four minutes, broccoli or cauliflower for five minutes and red onion chunks for six minutes. Grill starchy vegetables, such as squash and sweet potatoes, for between seven and eight minutes, or until softened.
Remove the vegetables from the George Foreman grill when they're soft but still slightly firm.