Heat gas grill to medium-high or coals in charcoal grill to medium hot. Begin threading kabobs. Beef Kabobs: Thread 1 beef cube, 1 piece onion, 1 tomato and 1 pepper piece onto a skewer. Continue threading until you have filled a total of 6 skewers. Chicken Kabobs: Thread chicken, pepper piece, zucchini and a different color pepper piece onto a skewer. Continue threading to fill 6 skewers.