For the red pepper relish, in a small bowl combine red sweet pepper, onion, cider vinegar, and black pepper. Set aside.
Coat an unheated 8-inch nonstick skillet with flared sides or a crepe pan with cooking spray. Heat skillet over medium heat.
In a large bowl combine eggs, salt, and ground red pepper. Using a rotary beater or wire whisk, beat the egg mixture until frothy. Pour into the prepared skillet; cook over medium heat. As eggs set, run a spatula around edge of skillet, lifting eggs so uncooked portion flows underneath.
When eggs are set but still shiny, sprinkle with cheese and chives. Top with 3/4 cup of the spinach and 2 tablespoons of the relish. Fold one side of omelet partially over filling. Top with the remaining spinach and 1 tablespoon of the relish. (Reserve the remaining relish for another use.) Cut the omelet in half. Transfer to two dinner plates. Makes 2 servings.