Alternately thread shrimp, zucchini and tomatoes on 4 skewers (If using wooden skewers soak in water at least thirty minutes prior to use.

Arrange skewers in 13 x 9-inch glass baking dish or large resealable plastic bag. Add 2 tablespoons Italian dressing; turn to coat. Cover, or close bag and marinate in refrigerator 30 minutes.

Remove skewers from dressing, discarding dressing. Grill or broil skewers, turning occasionally and brushing with remaining 2 tablespoons dressing, until shrimp turn pink, about 6 minutes. Sprinkle with oregano.