Coat a 10-inch nonstick skillet with flared side with cooking spray. Heat skillet over medium heat.
In a large bowl combine eggs, chives, salt, and cayenne pepper. Use rotary beater or wire whisk to beat until frothy. Pour into prepared skillet. Immediately begin stirring the eggs gently but continuously with a wooden or plastic spatula until mixture resembles small pieces of cooked egg surrounded by liquid egg. Stop stirring. Cook for 30 to 60 seconds more or until egg is set but still shiny.
When egg is set but still shiny, sprinkle with cheese. Top with 1 cup of the spinach and 1/4 cup of the Red Pepper Relish. With a spatula, lift and fold one side of omelet partially over filling. Arrange remaining spinach on warm platter. Transfer omelet to platter. Top with remaining relish.
Red Pepper Relish
In a small bowl combine red sweet pepper, green onion, cider vinegar, and black pepper.