Heat a small saucepan over medium-high heat. Coat pan with cooking spray. Add corn, zucchini, and onions to pan; saute 4 minutes or until vegetables are crisp-tender. Remove from heat. Heat a 10″ nonstick skillet over medium-high heat. Combine water, pepper (or Mrs. Dash), egg whites and egg in a bowl, stirring well with a whisk. Coat pan with cooking spray. Pour egg mixture into pan; cook until edges begin to set (about 2 minutes). Gently lift the edges of the omelet with a spatula, tilting the pan to allow uncooked egg mixture to come in contact with the pan. Spoon vegetable mixture onto half of omelet, sprinkle cheese over vegetable mixture. Loosen omelet with a spatula and fold in half. Cook two minutes more or until cheese melts. Carefully slide omelet onto a plate.