Coat an 8-inch nonstick skillet with cooking spray. Add oil; place over medium heat. Add zucchini and onion; sauté 7 minutes or until tender. Set aside, and let cool.
Combine eggs and remaining 5 ingredients in a medium bowl, stirring with a whisk until well blended. Stir in zucchini and onion.
Coat pan with cooking spray; return to medium heat. Add egg mixture; cook 4 to 5 minutes or until center is set (do not stir). Loosen omelet with spatula; fold in half. Slide omelet onto a plate.