Place cut vegetables onto skewers in random order (you may use more or less of any particular veggie; I LOVE the onions!) Brush evenly with teriyaki marinade; sprinkle with salt, pepper and garlic powder and set aside.
Make about 5 slits in each chicken breast and stuff a clove of garlic inside each slit (large cloves cut in half lengthwise).
Brush chicken with teriyaki marinade and sprinkle both sides with salt, pepper, and garlic powder.
Place vegetables and chicken on foil-covered grill at medium heat; turn every few minutes.
When veggies are cooked through and a little blackened, remove from grill and brush with additional marinade.
When chicken is cooked through and no longer pink, remove from grill and brush with additional marinade.