Cut beef into 1 1/2 inch pieces; place in large plastic bag. Add zucchini, mushrooms and bell pepper to bag. Combine tamari, sherry, oil and garlic in cup, pour over meat and vegetables. Marinade in refrigerator at least 30 minutes or up to 4 hours.
Soak 4 12-inch skewers in water for 30 minutes to prevent them from catching fire.
Drain meat and vegetables; reserve marinade. Alternately thread meat and vegetables onto skewers.
BBQ on medium high for 15 minutes brushing with marinade and turning frequently.