Whisk eggs and water until blended.
Cook and stir vegetables in large nonstick skillet sprayed with cooking spray on medium-high heat 5 min. or until crisp-tender. Remove from skillet; set aside.
Add egg mixture to skillet; cover. Cook 6 min. or until center is almost set.
Top half the omelet with vegetable mixture and cheese; fold in half. Cook, covered, 3 min. or until cheese is melted. Serve topped with salsa.