When putting together kebabs, whether it is a mixture of meats and vegetables or just meat of vegetables, the cooking times of each ingredient can be different. Proper planning can solve this problem. You can either choose items that will cook together at the same time or you can precook some items. I suggest that you time the kebab on the cooking time of the meat if you are making meat kebabs. A typical 1-inch cube of meat will cook on a hot grill in about 5 to 8 minutes.
If any item you plan on putting on the kebabs takes longer you should precook it before adding it to the kebab. Also, remember that tightly packed kebabs will cook slower than loosely packed kebabs so maintain a small amount of space between items, particularly the larger cuts of meat.