Make the marinade by combining the soy sauce, peach juice, oil, dried onion flakes, garlic and fresh ground black pepper. Whisk well to combine.
Cut the steak into 1 inch pieces and add it to a gallon size resealable bag. Pour the marinade over the steak, seal the bag tight and refrigerate for 1 to 6 hours.
If using wooden skewers, soak them in water for 30 minutes. Thread the steak and chopped vegetables alternately onto the wooden skewers, keeping a little space between each piece.
Heat gas grill to medium-high and grease lightly with oil. Grill the kebabs for just a few minutes on each side (8-10 minutes maximum), according to how well done you like your steak. Allow the kebabs to rest for 5 minutes before serving.
