Prepare mixed vegetables for kebabs by choosing vegetables with similar cooking times, then cut them into bite size pieces or lengths. Small vegetables such as cherry tomatoes are best kept whole. Green onions, fennel, red onion, eggplant, and summer squash would also be appropriate vegetables for skewering. Metal skewers come in a variety of shapes and sizes. For best results, choose skewers that are square or flat, they will hold food more securely.