Combine first 5 ingredients in a bowl, stirring with a whisk. Stir in roasted red pepper.
Melt butter in an 8-inch nonstick skillet over medium heat. Add egg mixture, and cook 3 to 5 minutes or until set (do not stir). Sprinkle with cheese. Loosen omelet with spatula; fold in half. Slide omelet onto a plate.
Top with salsa, and sprinkle with cilantro.